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the only reason why Frankie should learn
to arrest because in a two major
libraries of two major frameworks from
Apache like Apache spark an Apache Kafka
their major implementations in they have
written their implementations in Scala
and that's one of the major reasons why
Scala became so popular the last couple
of years and also there have been
various other frameworks like haka
framework in a like clear framework and
a lot of other you know a lot of other
database tools database management
relations mapping tools which were
released by scholars so that's one of
the reasons why Scala became very
popular in the last two three years
because of major frameworks we have
released now in this particular area
it's not only big data even in couple of
other criminal trial yoga or play and
even something on the thorium functional
relational mapping tools which have been
released and that's what that's what it
makes well a little scholar a little bit
more popular okay they're always asking
me that what about fighting with spark
how a real-time project distributed for
skyline right in between spark so are
always asking me that you know what
about by spark
you know the buy ten EPS was part and
how our projects distributed between
Scala and peyten with spark now there's
one interesting thing you know I I got a
I got a survey results from data breaks
data breach with the comp which was
formed by the founders of spark so these
people who founded spark you know the
founded a company called data breaks and
they did a survey this here 2016 survey
and it's very surprising that for the
last one year there has been a huge
shift in from scholar to baton so a lot
of people are actually moving to Buyten
when it comes to spark so and I'll tell
me the reasons later you know why people
are moving to Python gradually so and
maybe you should also have that plan you
know to learn Python as well but color
is important you should not rely should
notice call EPA's but having said that
you know I think the next one which in
which should be in your on your radar to
do the learning is basically
should have Python okay but I'll tell me
the reason later why python is required
and why people are gradually moving two
by two so here is here is the person who
is one of the cofounders of the other
languages name is Martino deskey he
works in a company called another
company he works in a in a university
called EPFL it's called a call
Polytechnique fédérale the Sun so
there's a place into Dillon Colusa solar
then he works in the school of
Polytechnic so it's called a called
Polytechnic federal so that's how it
works as a as a professor for computer
science and mathematics and he's the one
who came up with the whole in a grammar
and and the whole compiler design for
the scarlet language so as we can see
that you know Scala is a general-purpose
programming language and such an purpose
means you know it you can actually use
it for anything you want you know you
can you can use it to write spark which
is a cluster computing framework you can
use it to write a play framework which
is a web development framework you can
use it to write akka framework which is
an actor based concurrency framework so
it's a visual bubbles language you know
it it doesn't have any fixed purpose you
can just use it between one editor
combination as I told you before it's a
combination or different programming and
functional programming styles so now you
know what this means you know now that
I've explained to you so you know what
what these two phrases mean and this was
publicly released in 2004 on a JVM
platform and later a few months later it
had a release from the dot pen platform
so they started working around early
2000 and now we have pretty stable
religious as color which runs out now
here are couple of features of color
the first feature is that it's
statically typed language and by
statically dead language I mean that you
have to declare the type of the variable
and unlike languages like Python or Ruby
or JavaScript where you don't have to
declare the language integrated own
product particular the variable type but
here in Scala you know you have to
declare the type of the variable okay so
you have to tell the compiler what is
the variable type so that it can
actually do something meaningful and
it's xmoocs paradigm I told you it's
mixed by then because it fully supports
object-oriented programming concepts
it has function programming concepts as
well and just remember that everything
everything is the object in Scala so you
don't have a concept of primitive types
if you if you know Java you know that
you know Java has primitive types but in
fact there is no primitive types
everything is an object in Scala okay so
online Java Scala does not have
primitive types and you know it does
support a concept of static so we're
going to see that later in how how
static entities are achieved in Scala
and obviously there are you know
improved support life traits which are
very similar to Ruby modules we would
feed that later as well
and by mixed paradigm you know if you
look at the functional part we see that
you know it's a bot function programming
we are going to look into the features a
function programming later in the course
maybe in the next module and you know we
there is something called pure
functional programming so obviously so
there is not a pure function programming
language and like a scalar Ireland so
and I'll tell you why in a later when
you're doing pure functional programming
languages so solid supports also act the
libraries way which allows both mutable
and immutable variables so that means
you can you can use the actor's library
to create concurrency based actor based
concurrency models so people who are
interested in working on actor based
concurrency models can use the actor
libraries or scholar so actor based
concurrency is a type of concurrency
in computing so I'm not going to get
into that but if you're interested you
can just google on on the internet and
read or how it is actor based
concurrency and you know we're going to
see later that in functional programming
you know functions are first class
citizens so this is very important is a
very important term you know first-class
citizens functions are first class
citizens so this phrase basically means
that you know particular function or a
particular in Scala or in any functional
programming language a function is just
like a variable so that means you know
you can you can actually pass the
function to to a method you can pass it
as parameters to methods you can pass it
you can return it as values from method
you know that's what it means
so by first-class citizens I mean that
you can you can actually you know pass
functions as as variables
to admit that so it just be is like a
particular variable so you can pass it
as parameters to functions you can
return it as values and then you can
assign it they can assign it to another
variable and then call it okay so we're
going to see all these things you know
these are very exciting things about
functional programming and I'm going to
teach you how you can do that okay and
also Scala has a concept of closures so
closures we are going to see later it is
very similar to Python and Ruby concepts
of closures so people anyone here know
what closure is if you don't know it
doesn't matter you know I'm going to
teach you later
what closures are okay so that's about
scholar now let me tell you how
basically scholar works okay
so one of the major reasons was in the
developers were looking for flexibility
in languages to improve their
productivity because all the languages
learner they were becoming very heavy in
terms of in terms of the compiler in
terms of the code size so they were
looking for a lot of flexibility in
terms of data typing in terms of other
operations and that's how in the
scripting languages like Python Ruby
then Ruby closure all these things in a
become very popular and obviously you
know based on you know what we have
learned from scripting languages the
other day you know more optimizations
were done in existing languages so in
Scala basically Scala is an alien
language so all scholarworks is that any
other Scala code which you give it to a
scholarship Empire and that generates in
a byte code and this bytecode is the
format is exactly the same as the Java
bytecode
so this bytecode what you see here it is
basically Java bytecode and then you can
load this our bytecode on any JVM and
you can just run intense in as any Java
program so basically just remember that
in any Scala code whatever you write
finally you know it is when you compile
it it breaks down into Java bytecode
which basically runs on any njv okay so
it's actually 100 percent helium
compatible so that's how
Scala you know works so whatever we have
done so far any any questions you have
any doubts you would like to ask them
okay and these are in other frameworks
which I told you in which are very
popular and one is the one called play
clear framework if you so web
development
we already has part four in memory
cluster computing then we have a color
which is activist concurrency framework
and the other modules of neo4j which
have solar rappers as well as a
something called scanning which is a
MapReduce framework on scholar so there
are in a lot of things coming up and
even if you have in the latest versions
of Abacha Kafka that also has color in
ApS you know - for developers so here's
Ian Gosling is saying that you know if
you were to pick any other language any
language other than Java it would be
Scala so looks like he also likes Scala
okay so let's quickly now that time has
come to write code okay this particular
BM which I'm using this VM is already
there in your LMS you can download this
VM and install it in on a virtual box or
on a on a VM player and this particular
VM already has bark
do you know Scala and all the IDs
everything is installed there so you can
just download and start playing around
with it okay so let me you know Scala
basically comes comes with something
called the scholar shell okay so if you
people who are worked on bite and any
anybody who has worked on right then
okay they're always asking me is this VM
different from the Hadoop VM it may be
different because it had to be m ro you
know it has a bunch of other stuff
involved also liking so obviously what
whatever course whatever the teacher any
Hadoop cause those things is you know
installed but it's better to install
this because it just has a hug on this
part and Kafka and these things so it's
not very heavy
okay so choice is yours just checking
out in that particular VM if if this
part is already installed then you don't
need to work then you can just continue
working with the VM
because you need to get the same focus
anybody worked on a bite in anybody
knows fight in here okay basically see
the thing is that in a Python gives
something called a shell okay so there
is a shell called whiting shell well
actually you can do you know quick stuff
in a like in 1 + 2 3
so there's a bite in shell ok so it
takes you to there and you can do quick
computations you can write code
test code and test yourself and once
you're comfortable you can actually
write it in the source file save it and
then run it at this Python program so
similarly you know color also gives you
a scholarship so this is the typical
scholarship and these type of shells are
called repl shells okay just remember
that these are called in re PL shells
cooking repl means if you read you
evaluate print you in computer science
repl means read evaluate print loop
usually means that in a you type the
program the expression is evaluated and
output is printed and this loop
continues so that's what the repl means
and here you know we have an RPN shell
for Scala and so this div potential we
have and here you can write in a code
you can quickly test your code you can
save the code in and then once you're
comfortable then you can start writing
it in the IDE we usually you know in the
production code initially write coding
the ID but when you are doing quick
proof of concept or if you just want to
showcase something or if you just want
to see it for yourself you know just
want to do a quick test then you can do
B then Michelle is very very helpful
now initial image you can do a lot of
stuff ok yes raw eclipse can be used for
scholar so you can use Eclipse IDE let's
color that's absolutely fine then I'll
tell you how you know being I have to
using Scala Eclipse ID so this would be
skull ID and you can just type help and
see all the commands which are available
here ok and we able to use the shell for
a while before we go to the IDE now
remember one thing is that I I told you
that you know Scala is not an
interpreted language so Scala is
basically a compiled language so that
means you know unlike Python or Ruby
you know you there is no interpreter for
scholar so this color language is
completely compiled languages like Java
or C++ so what happens is in whatever
code you write in the shell and that
gets in a converted to a class file and
that code is executed ok so don't think
that in this color
shell is like an interpreter it's not an
interpreter so whatever code you're
typing and she'll have the background an
intermediate temporary class is
generated
and that code is executed okay and you
can see this color version here so
whatever color you are using so we're
using two 10.4 so you can see this
version here now you can you can use
this color you know as you know as an
interpreter as well and I think out the
later so so you know you can do things
like let me show it to you so you can go
to this color so you can just say you
know ten plus two it prints twelve here
and then you can say you can do
complicated in arithmetic on to nine you
know into 4 into 3 plus to solve this
single so you can do and now what I'm
going to teach you is I'm going to teach
you how you can declare variables in
Scala okay now there are this little bit
tricky but just be attention to me and
and see what I'm doing so when you
create you know there are two ways you
can create how very booths you can
declare variables in Scala one is
through using the keyword well and one
is through using the keyword back okay
when is the keyword well you actually be
clear and immutable babe so mutable
variable means that it cannot be changed
so just remember that environment it's
immutable variable so which means you
know it can be changed
so we're you know there are two ways you
can declare a variable is that you can
declare it as well which is called value
or as a variable var ver which means
it's a mutable really can be changed
later okay so that's how you declare
these are the two key words you use so
if I say declare X and this is how you
declare a variable so so whether you are
right you can see that you can view it
as as a constant and the way we declare
it is now you can write Val here then
you can give X here that's a variable
name then you have to give a semicolon
okay it's all you have to give a
Columbia and then if you give the data
type int int so integer int or float you
write float you put a string you write
string and then you declare and you have
to give the value here okay you have to
initialize it the value so then it
becomes an immutable variable white
immutable because now if you try to
change the value of 10 to 11 is actually
going to give you an error okay so just
a reassignment to Val so that means in
the valleys constant you cannot change
on the other hand you can if you declare
it as a bag then basically in it you can
you can make it middle so that means you
know this is quick immutable you can
change the values you can do whatever
you want okay so these are the two ways
you can declare our variables like in
color and also remember that you know
you declare the data type so you know
you can declare datatype make string and
you can write so this is declare that
string
similarly then you can declare float so
this makes it know it's all the same so
you can declare it as a float it can
declare it as double you can declare
this as boolean so this becomes true so
either various things you can do okay
with this and these are the variables
with you we should okay here if you can
declare variables in scholar and what
you can do with it so immutable
immutable types is this clear to you
what is the difference between bad and
battle now there is another another
interesting concept in Scala and which
he pollution is a
the stand is that NAU even if you don't
declare the variable type if you just
write it like this then basically Scala
what further if you in the figures are
the datatype so since you're only
rewriting true here so Scala know that
this this is a boolean type and it
converts X to boolean so if you do like
this it says that X is booking so please
don't think that you know Scala if you
don't like the variable type it does not
become like dynamically typed a lot of
people think that you know just because
I didn't write the variable type the
datatype for the variable it becomes
like dynamic type it is not animal type
it is called type inference in color so
that means based on what the value you
are initializing with you know it takes
a smart guess okay so if you write
something like this
so it knows ten is an integer all of it
it will make it as you know integer so
if you write ten point nine they don't
actually make a double because you did
not say anything so since there's a
floating point number so it converts it
to our double but if you physically want
it as float then you have to you know
write it as float okay so then it
becomes float
so if you physically want to float you
have to make it float or if you don't
give any datatype then by default it
becomes double so this is called type
inference ginger in scala and please
remember this okay okay this is let me
introduce you to any and it's going to
ask you a lot of questions from that
time so you just make sure you oblige
sure so here's the next is here's the
first question and he's asking you and
he's asking that is the scala repl acts
like this color interpreter is this true
or false
can you tell her whether which is a 42
correct answer
this is going to protect as a repl
actors call a interpreter yes you're
right the answer is false
very good well done class so the answer
is false because color is not
interpreter Scala is a compiled language
so even if it looks like an interpreter
internally the code is converted to a
class file and and the code is execute
so the answer is false
okay
you give answer the next question caller
supports primitives and Apple practices
true or false what do you think yes
you're absolutely right
Scala does not support primitive and
upper classes so the answer is false
okay so so now we saw in oh how we can
do variables and how we can declare
mutable and immutable variables so
that's exactly what's written here if
you want to pre read only constants you
can declare it as a valve this basically
means if you have Java as similar to
Java final variables similarly if you
have our let's say to read right that
means it's mutable and you can you know
assign you assign values to it and
obviously I told you about type
inference so that means even if you
don't give any type it's going to figure
out in what it is and it's going to make
a guess
okay so just remember that Scala is
statically typed language okay okay so
it's basically statically typed language
now you know let's talk about our
expressions and blocks okay so there's
another very important thing which you
know you keep in mind so say for example
in ayodhya 12 x equals to 10 in these
curly braces
I can I can declare actually values like
you know a equals 100 and I can write
well B equals 200 and then I can say a
plus B okay I can do this now if I do
this a a plus B then the value of x
actually becomes 300 okay so so here
what happens is it and you can write
expressions inside you know curly braces
and just remember in Scala so the last
expression whatever you're writing the
last expression
that thing is you know assigned to to
the video so that means if you have
something in a blog so if you have
something in a blog
so whatever is the last expression
you're writing so the last expression is
basically returned from the block and
here since we're assigning it to
variable X so you know this becomes kind
of return value for this work just
remember this is a very important
property of scholar you can actually use
it in several places which I'll show you
later and when you're writing you know
instructions in the same line you can
actually use the semicolon otherwise in
Scala you know the deadline delimiter is
basically a new line so that means in
Scala you don't have to give semicolon
like C++ or Java or C if you give a new
line so that becomes a new instruction
but if you're writing the instructions
on the same line you can actually use a
semicolon so I can write the same you
know instruction without using the
semicolon so I can actually write
something like this like new curly brace
I can say Val 8 equals 100 I can say Val
B equals to 200 and then I can say a
plus B
I can do the same thing okay this and
this is exactly the same
I just wrote it in separate lines so
that's why I did not have to give
semicolon whatever as you know in Ex I
wrote everything in the same line so
that's why I give a millimeter to the
instructions so which is a semicolon and
obviously the last expression in it
becomes the return type of this
particular block so that's how mythical
Escada works and this concert is very
important for functions and methods
which we are going to see later ok clear
all of you with this with this piece of
code ok good now let me show you
something called lazy evaluation ok this
is a very very important concept in
school again and now you'll understand
in a way scholar was used in spark now
you know the right spot let's say for
example I declared variable eggs in it
goes to 1000 ok now the moment I declare
it you know the memory is initialized
and now we can see that X is equals 200
so now if I say X into 2 it prints 200
okay now say for example let's
understand the business use case that
how in what is the problem with this
kind of stuff now say for example if
this X was a list ok this ex-soldier
list of say 1 million numbers and I want
to multiply each number by 2 so if I
just declared this X list equals 2 in 1
million numbers is going to take a lot
of memory right and so the thing is that
you know up front you know when i
declare the variable it's going to take
a lot of memories even if i don't use it
but if i have a requirement that i just
want to use it when I want to use it so
that means it's kind of load on demand
or just in time so then I can actually
make it as easy okay so I can write lazy
here so you see the difference between
this declaration and distillation here
when I declared it it straightaway shows
100 but here it doesn't show hundred you
know it just shows lazy so that means
actually no memory has been allocated to
this particular variable and these are
very very useful you know when you are
doing very large computations that means
a front you know you don't want to
commit to any memory you only commit to
memory when there is actually some
computation you're doing so that means
when I actually do an X into 2
that is when you know the ex is going to
get initialized 200 and and the value is
going to be computer okay so there's a
very important feature of Scala and many
intervention languages has this feature
it's called lazy loading or on-demand
load loading and in the difficult are
usually when you're doing large
computation so when you don't want to a
front in allocate the memory but you
just want to do it on demand and these
are very very useful for cluster
computing as well because in plus the
computing you know if you have various
computers in your network and just
imagine you know if you just want to in
a load
say for example a list with you know 1
million values and you want to send it
across in all the clusters it actually
you know takes a lot of memory lots of
in our network in which happens so
rather than that you know what you can
do is you can just declare it here and
and it will be actually sent when you do
some computation on it ok so it's like
that so it's always on demand so 11 you
are you know you're doing the
computation that's when you know the
value is initialized and center of the
computers and the computation starts so
that way you save a lot of memory you
save a lot of network bandwidth and you
can do a lot of optimizations in this
one set ok lazy 12 a few and that's one
of the reasons why you know Scala was
chosen
you know to write this cluster computing
plane works part it is that way you know
it could optimize because otherwise in
if we just declare upfront you know
these memories allocated and that
becomes a big problem
ok ok Praveen is asking me that can you
give me an example with multiple values
of X yeah sure I can give you but the
thing is you know you still haven't
learned collections so I just give the
example but maybe later on you will
understand what I am trying to write
here so I can just declare a list you
know a list of say you know want to say
I can say 1 to 100,000
and I can see so here are generated a
listing of one 200,000 and so is leaving
one 200,000 and generating the list it's
a list of integers with so many values
here okay I'll front you know so many
100,000 integers allocate but I can
optimize it in I I can just optimize it
and and now say for example and if I
want to you know find the sum of the
list so I can say don't worry about the
syntax you that's what you're going to
learn later now you see that in if I
want to you know finding you know sum of
all the integers in the list you know I
can just do this and this is the number
so you have hundred thousand numbers
here but just imagine in a few millions
and millions a number it will be very
inefficient and you in a straight away I
look at a lot of memory to it so what I
can do is you know I can just declare it
as lazy so then it becomes is that when
you actually do some computation so when
you actually do a computation that's
when it will be loaded so now if I do in
if I just want to find the sum of all
the numbers in that case you know now
you see that you know that times actual
memory is allocated okay yep ready ok
Xin USA is asking me this definition
will store in memory rather than process
immediately as you are actually verso
basically the definition is stored in
the memory it is not if the instruction
is not immediately executed you know it
is just or the instruction is executed
only when the first time when you
reference the variable through some
computation so when you actually do some
computation that's when the value gets
referenced so this is a very important
concept lazy
just remember this because when you're
actually doing SPARC architecture you
will see that this is this has been this
one um be in cornerstones of the SPARC
implementation so maybe you know you can
just have a look at this example and if
you have any questions for me nasty I'll
just give you you know just 30 seconds
or maybe one minute just take and just
recollect whatever we have done in the
last one
R and T in a few if you have any
questions about chicken ask me okay
Irene is asking me that could you access
the value without any computation or
will you can do that the moment you
access the value it's actually you're
accessing it okay so in that case you
know it's the immediate in the value
would be in a loaded into the memory so
the moment you actually in access the
value the definition becomes a
manifestation clear Irwin okay
so go Vanguard if you have joined late
don't worry the recording will be
available in the LMS so you can just
check the recording and you want to
understand what this is syntax reduce
I'm using don't worry I haven't
explained it to anyone because it's just
an example I was giving but we are going
to learn about the syntax when we are
doing functional programming so not only
move it's not but this reduce just takes
a some you know to find out the some of
the list
don't worry about the syntax but there's
what the reduce function does okay and
you can use lazy for you know for file
loading anything you know so if you're
loading a file you can for any kind of
operations okay okay are always asking
me is this reduce function similar to
the MapReduce it's not similar but the
conceptually they are the same because
when you do in the reduction phase in a
MapReduce whatever happens in this
function also the same thing happens but
conceptually they are similar but and
they are not the same okay okay Praveen
is asking me if you want to apply some
logic on individual members of the list
so if I remember it may load the list
right yes you're right Praveen
if you want to individually apply some
computation to a cell in a particular
list he cannot do that
the moment you access the list the whole
list will be loaded into the memory okay
right so now we are going to see some
if-else statement this is an I'm not
gonna spend too much time on this
because I think all of you know this
nothing is you know you can you can
desert if Akali fence
structure so if you can and a boolean
you can give a double ampersand for hand
or two bytes for a logical or and you
can give in a boolean operations like
this okay we will is asking is this lazy
concept similar to the big concept
absolutely similar a similar it's the
same concept you know which which
we are going to use in spark and they
also in spark also there's a concept of
tag so the dag actually is are not
nothing but an easy initialization so
Vemula it's the same thing okay go do
you know that at least that we you you
can really be able to relate ok so let's
see if PES part and now we will look
into some important stuff called loops
ok how we have a loop a particular
invite relations so say for example in I
declare a variable in an STR called test
ok so here we have a test and just
remember that in every every iterator or
every collection has an implicit
function call for each ok so so the for
each what it does is you know basically
inside the for each you know you can
actually give a punch so what happens is
this is what in a function programming
is all about I told you that in
functional programming functions are
first class citizens so there's a
function called println okay so this
println basically just like system dot
out dot println in java so it prints on
the console and you know you can pass
this function as a parameter to another
function call for each and so this
fourpence forage is going to do is it's
going to print every element of this
collection using this println function
okay so that will be for each you know
does and and i told you that you know
for each you know is available to any
collection in scholar and string is also
a collection because you can see a
string you can view a string as a
sequence of characters or at the list of
characters so you know you can apply
this for each loop to in to any
collection so that's what you know
first-class citizens in action so that
means you know you can pass this for
hvcu takes a function and you can pass
any function you know here which
basically and here is the print function
which is prints without a newline
so the test is printed
you're going to see the more of this for
each loop you know when we are doing
lists when we are doing you know when we
are doing any kind of collections little
later okay but just remember this
particular function for each I hope it's
clear right what for each is doing and
you are able to understand this okay now
we are going to see the for loop the for
loop in interval a little bit different
from the for loop you know in C C++ or
Java so the for loop is written like
this and this is the general syntax so
here you write the argument and and
there then you give an operator like
this and then you give the collection
here okay and then you write whatever
port you want to write so this is a
typical where you want to declare a for
loop so here say for example you know I
I can write something like this
so here this is what this what
for loop does is just a attention is
that I have a list in from one to five
so if you just write one to five on D so
it will generate a range of numbers from
one to five
so those are going to collection it's
part of the collection so what it does
is it I takes each element and this
buddy collaborator it assigns each
variable of each element from this
collection to a high and this is printed
okay so so now you have from one to in a
five you can print each of the numbers
so similarly you know and by defaulting
on the numbers increases from you know
by one so now if you just want to run
the loop or in the opposite way if you
just want to say you know five to one so
that means instead of drinking one two
three four five you want to print five
four three two one
so this is not going to work because by
default in on the loop increases by one
so then you have to say by minus one
okay so this basically means that the
loop counter is going to decree with my
minus one so it's this remember this
particular syntax of the for loop
okay error here you know raw is asking
me what are this rest nine and you know
then I'm seeing ratifying what are these
stuff so these are temporary variables
which are created okay so so say for
example if I write this I told you that
you know this code is converted to byte
code and it's loaded in a class and
executed so the return value is stored
in a temporary variable called result is
basically result in not result and it's
a serial number one two three four five
like that it's a running counter okay
and then so that's what it so temporary
it's a temporary variable in which
variable to store clearer okay shelia is
asking me can i have any other increment
here why not you know you can you can
give minus one you can give - to give
anything you want so this just prints
the odd numbers okay so basically you
know it just strings the odd number
similarly if you want to print the odd
number in the reverse way so you can
just say in one to five by you can say
to safely print
here's a leader so you can do buy
anything and I just like a four loop
counter
okay shanira's is asking that just a
quick question can I use minus one for
each no in the for each I told you that
before each you cannot pass other than a
function you cannot anything okay so the
for it only takes a function and a
foreign to know we usually use for
collections which I'm going to show you
later but usually for the general
purpose for loop this is what we
typically use okay okay before I went to
we went to a break
Vimala was asking me that for she was
asking me this okay so let me write it
down she's asking me that what happens
here okay so why is nothing been printed
so what do you think what is happening
here others would like to try what the
Millers question is that you know this
particular thing doesn't print anything
so what's going on here yes sir oh you
are right we will any any guesses does
this make any sense at all because you
are you know you're reducing the counter
from you know five to one but you are
incrementing it is this possible like
it's kind of contrary condition so I
just tell you it's like it's like
telling you that can you climb from you
know from first story to the third story
by climbing down okay so this statement
right cell doesn't make any sense got it
right it's not infinite loop it doesn't
make sense
I track telling you that you November
you go from first flow to third floor by
stepping down
I don't know how is that possible you
know if you only can you can only go by
stepping up right by stepping down you
cannot go from the first row to the
third floor it's like that okay
nothing will happen actually because the
condition is purely false you know so it
cannot do that you know because ranges
from five four three two one
and you're trying to increment so
obviously this whole condition is false
and that's why this is never printed
okay so give them less so the kind of
false fault condition okay okay right so
that's you know that's about so no
pressure and we won't have any exception
you know there's not an exception
condition is just that the condition is
false so obviously it's not evaluated
okay so that's why you know it never
happens okay and you know you can do in
a loop you know this this one level loop
you can also do two level loops like
this so then you can you can run a loop
from I say you know one to five and you
can run J from say 1 to 4 and you can
print you can print something like this
okay
Topol i j again and
here's one syntaxin 'you should pay
attention to see inside the string okay
inside the string I'm referencing you
know I and J so you can reference in a
variables inside a string but you have
to just prefix it with the dollar okay
so if you prefix it with the dollar so
Scala knows that you know this is
actually a variable which needs to be
substituted at runtime and how it is to
be substituted as a string so that's why
I put s here okay has a string if you
want to interpret it as an integer so
you can give a D here also no Big D so
you know but the D is not going to work
because you're putting it in the inside
a string okay so that's why in a year -
you know to put it s in s so that means
you know just convert this integer to a
string and substitute it in this
particular string okay so if you want to
get embed variables inside strings you
have to put a dollar before the variable
name and images outside the codes put an
S so which means that you know convert
these variables to strings and then I
met them yeah so that's how you you do
this okay so that's all you do in order
to to level and even go up to three
level four levels like that there's
another important condition you know
which which I would like to tell you and
these are typically bad conditions okay
so now if this is this loop clear to all
of you this particular loop clear to all
of you can I have a good poll on whether
this key or not
okay so this is how I end up in my
particular loop now I can write the code
like this also now the thing is that
what if I just want to print only when I
equals to equals to J okay so so I can
write the loop something like this okay
so I can write that in a for loop then
you know I can write an if statement you
know if I equals the equals to J then I
can say you know print this okay and so
then it will just print for I equal to
equal to J okay now this particular
inner loop is little bit inefficient in
the sense that you know the iteration
basically you know happens here because
why the iteration happens is because you
know for every you know iteration it
basically goes inside the loop that this
checking and based on whether the
checking is true or false you know it
does the computation but inspire in
scholar you know you have a between a
very nice feature and the feature is
that you can directly write the if you
know if you have a guard condition these
are all God conditions unique and very
active in in the for itself and then you
can just say in a println you can just
do this okay this is this is very very
efficient and then this particular piece
of code because here in the iteration
itself you know you know it can do a
check and based on whether the condition
is true or false it proceeds with the
loop because you can actually put a bad
condition here and these are very
important in when you are doing any kind
of processing in your in your business
logic so say for example you know if you
have things like if you write a loop
like you know for say for example for
every customer okay from the customer
list you are taking and suppose you're
doing some processing okay you are
you're doing some in the processing of
the customer and you only check that you
know you only enter the loop you can say
that if you know customer dot is active
so you can't do something like this in
your life if the customer is active only
that means him and he's not hibernating
somewhere in Siberia so that's the case
then then only you proceed with the
processing
otherwise you know you can just keep on
going through the customer list okay so
all sorts of you know in a predicate you
can add here so this one business use
case in practical application I showed
you which is very very useful you know
in linear processing clear all of you
did you did you all understand this I I
want you to understand you know this
thing very clearly because I'll be using
this inspark a lot and it's important
that you're understand this as well as
the lazy thing that the lazy is very
very important that's the cornerstone of
the SPARC architecture and I want all of
you to be equally competent on this ok
Praveen is asking me does this process
have any meanings having if n for no ifs
basically means that you know if the
condition is true then only you know the
chain of the code inside the for loop
will be executed as it skipped okay
Praveen okay what do you mean by Praveen
any naming i/o you mean is does it have
any name is that what you mean pravinia
it's called a dot condition okay it's
called a for loop with the gaud
condition I said that you know when I
was introducing you to this it's called
a for loop with a guard condition okay
universe is asking me okay no problem
Praveen you know it's quite possible
because you don't see me you know you're
hearing my voice it's quite possible
even without things no problem
the universe is asking little bit on a
little bit more on is active no exactly
means that you know I'm just checking
whether the customer is active or not so
say for example I I just want to send
some bunch of offers in or some free
gifts to my active customers so so if
only the customer is active then only
and I do the processing from the
customer list as I escape okay so that's
what it's just a simple example I wanted
to give you so instead of is active you
can have any other things like whether
is the customer a premium customer or is
the customer you know saying in some
particular part of the world okay yes
shinu SH right I just write it down it
in case there's a problem with my accent
and people don't understand it's called
a for loop you know with a god condition
okay so that's when you write a for you
know with an F inside okay yeah yes
Geneva that's right so now it's better
to write it down at times because you
know English has many in a homonym so a
lot of words sound similar so it's
better to write it down so that we all
are in the same page okay okay yep so
once again let me see if I've answered
all the questions okay now Erwin is
asking that can you use this if in for
each so yes we can use this in for each
I'll let I'll teach you later I mean
when we are doing functional programming
because now in our IDE a lot of syntax
which you may not understand plus I want
to give you some more fundamentals on
functional programming before I jump
into you know on the usage so I don't
want to rush into that you know so we'll
do that in in the next module for now
and I'll just stick to this example okay
but I'm going to make it more
complicated later on and I'm going to
tell you exactly how you should do it in
production code okay that's what you
should do so but since today is the
first thing I'm just taking a little bit
easy okay okay a Rafaela is asking me
that so just to clarify if I put that
condition inside the for loop it's
always more efficient yes or firelight's
right if you put this
inside the for so that's called a
predicate if you put that very good
inside it's always much more efficient
you know then putting the predicate
outside the fog okay okay I did I get
your name right a fellow or you want me
to call you MA or fella or just let me
know okay Inderjit is asking me can
nigga me can you give us one more
example with regard condition one more
condition with the god condition these
are typically in your typical checks you
know which you want to put inside as
I'll give you another example very very
simple example though so say for example
if you just want to print here maybe
even numbers from the list so say for
example you have this for loop in
running from 1 to 20 and you just want
to say that in a if I in a modulo 2
equals 0 so that means only if the
number is you know even then only you
know you print the number else you don't
print the number okay so that's
basically an example for even this is an
example for odd clear in digit yes
Geneva says I'll tell you now you know
which is more efficient I'll I'll tell
you like here I told you what is more
efficient so as I go along and I'll tell
you what is the code you should write
and what is the code you should not
write okay so so that I will go as I go
along and so now let's understand one
more thing okay so here since already
give this example here so here what we
are doing here is you know we are
collecting a in a we're just printing a
list of you know we are printing all the
even numbers from which occurs between 1
to 20
inclusive okay so this is what we are
printing
if my requirement is that you know I I
want to collect it in a list so instead
of printing because he in actual program
you don't print read you you collect the
results somewhere and then you do some
further processing on that so instead of
printing because printing is pretty
silly you actually don't do that in your
life coding so maybe if what if you want
to collect all the numbers here you want
to just collect it in a list and send it
back so for that you know we have
something called a keyword called yield
okay so you can use the keyword field
so in ield what happens is ad is a
keyword and so here basically the output
of every volume by duration is stored in
a list okay and and it is basically sent
as a vector so you can actually collect
this in the inside in a vector and now
you have X in a which is so instead of
printing you know you can just you know
collected in a bank vector and then you
can do some functional computation get
run so remember this you know if you in
case you want to collect some operations
somewhere so you can actually do this so
say for example the previous example I
gave you about the customer thing
looking so we were doing that you know
if you know if the customer for you know
for the customer list
so if another customer is active then I
can end another customer okay
so then basically I will have you know
so then what I can do is I can actually
have a list of active customers okay if
you want to list of active customers you
can do like this so you can go through
the list of all the customers and only
if the customer is active then you keep
storing it in our vector and and that
you assign so then finally you have a
vector of a list of active customs okay
so that's a practical application of
typically of using an eel okay
so just remember that in the yield you
know the results of the for loop so just
to summarize in ield you know the result
of each for loop sorry iteration is
stored in the list again this is a
vector to be precise and is very useful
I I showed you when typical example
where you can use this here all of you
what with what ield is what it does okay
good so all of you are clear with this
now let's you know understand functions
okay so now we are going to talk about
functions in Scala how you define
functions so from the morning in a way
we have seen variables key words like
Val which means an immutable variable
okay Geneva yes you're right
yield is only usually applied with the
for loop so obviously know since you're
collecting the results in an iteration
so so obviously know it goes in it goes
hand in hand okay from the morning we
solve Val which means if you want to
create immutable variables if you want
to create mutable variables you use var
now we are going to see how we can
define functions okay so here is the
standard you know syntax for functions
so you write def then you have the
function name
then you have another function
parameters and and then you have the
return type and then you write equals
and then you give the braces okay and
this is where you write your code
so this is the standard in a typical way
we write in the function so we read the
function in the function parameters and
the return type so let's look at an
example so I'm writing a you know
function to calculate the area of a
rectangle so I can say length you know
which is an integer well let's keep it
float okay so this is my link and this
is my bread B which is again a float and
you know it returns into the float the
results and I can write linked into
bread okay so that's my function so if I
want to write in a function to calculate
the area of rectangle so I say def the
name of the function area rect then I
give the parameter list so I write the
parameter name then give a colon and
then give the data type and then then
with the commas you know I keep on
writing and finally the parameter list
is over and then I give a colon and then
I justify the return type here then I
write an equals sign and then within
braces I write the code now I totally
know in the beginning of the lecture
that you know anything written inside
the braces you know the last expression
here it's only go it's only it's the
only expression here but usually the
last X question becomes the return type
so here basically you know this becomes
a return type so actually in Scala you
know you don't have to write something
like this you don't have to do this
unlike Java or C blessed with
the last expression by default becomes
the return type becomes the return
statement
so the length integrate is defined okay
so so this is the one which we have here
let's taste it you know in the console
oh this was float sorry
so then I write linked into bread so my
function is defined so I have a fun you
know area function call area rect and
the parameters is linked in bread which
is of type float and the return type is
float okay so now I can call this
function Ling area rect
and then I can pass 10 a 9 it sends 9
organs a 9.5 and arrogancy 10.23 so so
this is taking float on us to float so
this is a and here I'm writing F because
you know by default
it tends it as a double but since my
function is only taking float here so I
write f so f basically means that treat
this number as a float okay so so this
is my function which I've written here
and you can write various function so
you can you can write even so this
particular function is returning a float
okay so you can also modify this
particular function to not return
anything okay so so say for example you
don't want to return anything in that
case in a you write unit so when you
write unit it means that in your
function doesn't return anything it's
like a void function okay so you can see
in del n if you just want to print in
the area
so then you have a function called a
redirect and now if you called
so it just drinks you know the number so
here the function is not returning
anything it's just sprinting so then the
unit basically means acting and the
function doesn't return anything so it's
a void return type okay clear all of you
with this unit stuff how to define a
function okay now that you know all of
you know that can you quickly tell me
can you write the code for me if I want
to check a function say whether the
number is even or not so if I want to
write a function call is even number so
I just want to check whether the number
is even or not can you tell me how the
function is going to look and here I'm
going to pass you know a number so I'm
gonna pass and it's going to return a
true or false whether you know whether
it has it is give a number or not so can
it tell me how I'm going to do this can
you write the code for me let's see but
whatever you've learned today okay let's
see what what things we have here
brilliant
Ramola brilliant okay Rena let's see we
know what you're doing
we don't need that if Rena so without
the if it's fine well done Rena yes your
code is going to look something like
this well let's see what Praveen is
doing no Praveen this code is not going
to compile okay I'll write the code in I
have all sorts of stuff here so this is
the best you know we're checking right
so I'm going to write it as is even okay
and this is the number and there's a
boolean and just here I write number
modulo 2 because 2 goes to 0 because
this expression is the boolean
expression right there's a boolean this
will evaluate to true or to false okay
so in that case inner you you obviously
have there's a boolean outcome so
obviously now this will be the true or
false and that's the best way to check
well done for the people who had written
the code like this is the most efficient
and the best code which you can write ok
so just write this number modulo 2
equals 2 goes to 0 because this by
itself is a boolean expression so it can
either evaluate to true or false
okay sure ledger what have you done yes
you're right earlier it's the same stuff
which you've written okay okay now
Praveen is asking me that if I want to
if how I'm going to do it okay so the
thing is that it is the best stuff but
if you are if you want to use if so I
said no I want to use it even though
it's not the best so in that case then
you have to write like this okay you can
write it number equals equals to zero
then you stay true else you say false
and then you close the number okay and
then you say
oh boy okay thanks for okay Praveen so
what you don't need to write like this
of this so you actually the best way you
can write it okay so but it's okay now
it's good to learn do those okay so one
thing you notice here that we don't have
to write return here because that's
really not required so so that's one of
the fuzzy things about this language
okay good so I think all of you have
learned how to write function and this
is all what is there you know in in
functions if you understood this basic
part you know that the basic thing is
that you know how you declare a function
with a parameter list what is the return
value and how you're going to return the
value I think you've learned that you
know there's nothing more to it now it
depends on what kind of functions you're
writing and what you're doing there okay
but otherwise it's absolutely fine okay
now one more thing which we are going to
learn here is about arguments okay so
let's go back to our function in which
we wrote here oh yeah probably I'm going
to tell you that little later okay so
let's go back to our occasion Ivana is
asking me what is the issue with my
syntax okay one sec let's see what
you've done not surely whether this
stuff is not going to work right will it
will it work what do you think no I
think the best thing is you know just
check it out in the just check it out in
the console because you know I don't
want to sit invalidates in tanks with is
that that's what really wastes my time
so but if you have any fundamental
doubts you can ask me and I'll be more
than glad to help you okay good so let's
go back to in addi area thing and I'm
going to teach you something called
default arguments okay so I'll just give
the function definition simple so that
we can focus more on the learning and
rather than get stuck with differ types
so here's the function I have in an area
wrecked so I can call this to this art
works now you can keep default arguments
okay so here by default arguments I mean
that you can actually set say you know
birth to ten okay if you do that then
when you call length you know so you
just have to pass the value of length L
as 10
because bread by default will be in a
set 200 okay so so that you can do and
in case you want to overwrite the value
of bread you can give 12 here so instead
of 10 12 will be used so now it's 120
now there are a couple of rooms you know
in there couple of rules in in setting
default arguments the thing is that you
cannot set default arguments like this
okay and this is more or less in a true
for all languages so you cannot do like
this if you do like this you know there
will be a lot of confusion so say for
example if you define a function where
in the first argument the length we are
defined defaulted to 0 and then the
bread you know you haven't defaulted to
anything now when you try to call it it
basically complains because it really
can't figure out in what is this 10
should it assign the 10 to the length
which already has a default value of 10
or should it assign in a children assign
10 to B which is the bread so then the
compiler complains one way you can solve
it is that you know you can write B
equals to 10 okay then in that case it
will work because it knows that L
already has a value 10 we should be 10
then okay so you can do that and you can
act your code but if you don't do this
then it's going to complain but this
kind of coding is actually a bad
practice I don't recommend and what
color best practices recommends is that
when you give default arguments make
sure that you know you give the default
arguments at the end okay so don't give
it at the beginning but give it at the
end okay so that you know you don't you
know planned up in writing things like
this okay but having said that you know
you can have a default argument in the
beginning and you can resolve this by
actually you know telling which argument
is what but that's not a good practice
okay even though the compiler allows
it's not a good practice good practice
the best practice is that you define the
default arguments at the end of the
parameter list okay and then once you
define like this then you know you can
call area rect
then dips works it works perfectly
let's start now you know Scala has a
rich collection of it has a very rich
library of collections so the
collections you know which we are going
to primarily focus on and which are very
important for you are arrays array
buffers Maps tuples and lists and in
most of your career or in context or
programming image you're going to use
either of the five and they are very
very important so I'll tell you how to
used so first thing is in a way would
use as an array or now an added is of
fix I slept in so you cannot change the
size of net and this is how you are in a
declare an attic so before we can use
the class let me show you the class
first so if you go to those color Docs
and type Mary so you'll see that this V
and you've got in this color package
these are the method you know it has
okay so you can go through the methods
later on and figure out what are the
things you need
so let's use the Annie
so you declare the area's new then you
write a day and the thing is that you
know whichever package in a vision is in
this color package so whichever class is
in the instance color package you don't
have to important so it's just like the
java dot lang classes in the Java doc
language they implicitly in available to
all the classes so similarly Scala in
whatever classes come on this color
they're all available to the compiler
the theorem that important to be good so
we ready and then what you have to do is
you have to specify what the array
stores because you know in in color just
like Java or C++ you can only store
homogeneous objects okay so in this area
we are going to store integers so you
mentioned in square brackets integers
and then you have to mention the size of
the array okay so so this is an array of
integers and it's going to store 10
integers okay and all the elements are
initialized to 0 and you can access the
array you know with they are all the 0
based index ok so you can see that the
arrays are zero based index and this is
all you access be an in with the normal
brackets
and you know you can set the value to
the array like this
ARR 1 sorry equals 200 and now if you
print the array you can see hundred 200
like that okay and if you want to print
each element of the array so you can say
for each println which you have already
learnt in the first module sorry in this
module so it's going to print all the
elements appearing scare how you or
declare an array the similarly if you
want to declare or you know an array of
strings say declare an array of strings
and you see
scenario 3 strings declared to null
and you can initialize them to test and
is another fourth route okay yeah
and the thing
one way of declaring an array in a new
array give the data type and the number
of elements you want in the array or you
can start again with acuity re so rather
than giving anything you can just right
at it and the very latest an array and
you know give the elements inside it
though will naturally we want to doing
such things in programming because the
data is usually interpreted not by a
program obviously you'll never hard code
the data but in case you are testing
something you know just small things you
are testing you can also declare like
this okay so and then you like this as
well
okay so both are valid but usually this
is a statically declaring the area which
you're really doing the program other
than testing stuff most of practical
issues you'd be declaring it like this
okay now I would like to ask you one
quick question have you understood this
whatever I've done it'll clear any
questions you want to ask me okay now
I'm going to ask you one question and
the question is that you know you you
see that the way I have declared the
array we can take libya's well ARR
equals two new array of strings element
3 now this ARR is a well okay so that
means it's immutable okay every right
VRR is immutable and if that's the case
then I'm able to add you know values
ruler to that integer stuff okay it
declared integer Ally as a Val and then
I'm able to add elements to this you
know because yesterday we learned that
well you know it was immutable so that's
the case then how am i adding elements
to this particular thing any ideas any
hope you're always saying that the
number of elements in the array is
immutable
no that is by definition you know an
area by definition and the site is fixed
so that's not a big deal but what I'm
saying is that you know I'm declaring
this as well how come I'm able to sign
it okay pravin is saying that after
initialization you have assigned a value
so if you redo it may that's writer
write won't throw error you know I can I
can again you do this stuff I just work
so then you are
it's not the size of the area which is
by definition size of the array once you
declare it immutable I'm saying that Y
is the ARR reference now you know it's
still kind of you know I can change
values entry okay thank you all for your
answers let me give you the answer here
the trick is that you know when you
declare objects as VL as as well as
basically the object reference we
continue to okay that doesn't mean the
object is in YouTube so you can have you
can change the object value you can you
know you can change the state of the
object but the reference remains the
same okay so you won't be able to change
the reference so that means the error
will always point to this particular
value you know this particular hurry
okay so I can give you the example here
to say for example you have this area
here
now you cannot do this so error will
always point to this particular area of
1 2 3 4 5
not actually now do this okay you cannot
write air and now you know under to it
if you try to do this exclude give an
error so that means this particular
assignment this reference remains
constant gear out of you so remember
that you know many poor cases of objects
and containers so the reference it'll
always point to this particular either
you cannot change the reference but
having said that you can change the
value that's that's very much much more
ok so just remember the fundamental
difference with in general objects an
array so for example if I write x is
equal to 10 so here what happens is in X
is always pointing I always having a
reference to them you cannot you know
change the reference of X from 10 to
something else and for this for this
also you know this error is always
pointing to this collection area okay so
you cannot change the reference however
you can change the contents of the
adding you know that is quite possible
no problem with that
ok yes now you're right so individual
elements can be changed by in a by
accessing the index ok talk about
anything that how do i define an array
with a set of where the values are
constant see praveen if you want to
declare an array with the values as
constants then obviously up to
individually now you have to insert in a
value which are immutable ok so
but generally by definition you know it
is not possible in a days you know
that's always college designed because I
really don't get a use case that what I
you want to do such a thing because you
know in a collection you're going to
store value so why do you want to store
constant you know stuff in the
collection in that case you can just
keep that in a variable right so Scala
actually does not allow this even Java
does not allow this sense because there
is not real good use case for this in
business ok so so that's about you know
and it's to remember this is a very
important thing so now we go to
something called area buffers so the
only difference between a 10 and a
buffers is that it has a variable length
so it can actually grow okay so let's
again take an example I can declare an
array and you have to mention what is
what you're planning to store there and
you don't have to mention anything in
the racket the size so basically you you
get an area buffer what happened a
debuff and not found so I have to import
import color collections not beautiful
not add a buffer okay okay so you can
put this color collection you don't lie
buffer
you can declare this array buffer okay
so we have this item over here
and elements to the sorry bathroom like
this
so hundred has been added now 200 has
been added and even also you know add
like this as well you know you can say
300 400 so you can do like this so now
you have an array of okay Charlotte is
asking me a question I didn't understand
what's the question okay and you can
also you know so we saw that this is how
you can add you know any elements to add
a buffer and also you know you can if
you want you can straightaway add you
know an add a also to the area buffer
sorry plus so now you can see if you
want to add individual elements in you
can you can use the plus equal to
operator and if you want to append
collections in it to the existing area
buffer you can use plus plus okay okay
surely guys I'm just trying to our
understand what sirisha is asking me
disco-pop well here okay silage I think
that she's trying to understand services
trying to understand the scope of Val
and bears in terms of Mary see the
things that you know when you make an
area pal
can you hear all of you can you give Mia
okay so when you make it a bath so that
means it will be constant the reference
is constant and when you make it back so
that means you know the reference can be
reassigned to another
inner to another area or something like
that okay okay you want an example
actually I explained it to you another
way you are still confused
we have this area and we have this area
which is at a buffer now the thing is
that you know if I if I declare another
you know I cannot do this because I
won't be able to reassign it you know I
cannot write a de buffer so that won't
be possible you know I cannot do this
the tears in reassignment is not
possible but if I declared this error as
well then a reassignment would have been
possible okay and Ajit is asking me that
creep please explain explain result five
and that is a dark 15 yeah what we'll do
is it well let's quickly see the e in an
array before class so if you see the
area before class even co-operators okay
so you will see the pathless operator so
what the plus plus operator does is
basically you know it creates a new
collection containing both elements so
if you look into this definition it says
that and it creates a new collection
containing both the elements from this
collection and the provided collection
so that means what I am doing here when
I'm doing a plus plus so basically it
creates a new era buffer and you know
with the old values as well as the
values which I'm providing here here in
digit so similarly when you do a plus so
that means you know what happens is you
can append you can append in an existing
collection to the error so let's look at
the plus now so if you use a plus it
says that in append a single element to
this buffer and returns the identity of
the buffer okay and similarly know like
just apply just like plus plus you also
have minus - okay so this basically what
it does is it just a complement of that
so
you know whatever you know elements are
there any that will be removed
okay whatever is in the traversal so
I'll give you an example here so here we
added you know this particular thing 600
ton hundred eight hundred so this is my
new add a buffer which I have I can I
can right now if you want to get rid of
700 800 you can give it like this so now
you see that you know from the old daddy
700 800 has been removed okay so I think
that sort of Carl was asking that is it
possible to subtract to remove values
from a new buffer so exactly this is how
we do it okay care carne and similarly
now you have the - is upgrade also I
think if you want to remove individual
elements from these again and then you
have a bunch of other utility matters
like if you want to append to the string
append to the collection if you want to
clear the collection so let's look at
couple of other operations which are
there so on operation we have in
yes universe I'm just coming to your
questions only so this is for random
stuff you know and the same some
cooperation just are in a you have
something called a dream end so trim and
means in I'd will and these are all
applicable to both added an edible
possibly it's not only applicable to
adage is they're applicable at above us
as well okay so to tell you that in a
when you call cream end so this removes
the last two elements okay so it goes it
goes there and calls the last two
elements and it's just like this and you
can you can say ARR dot cream and so now
if you print error you will see that 500
and 600 has been removed okay so these
two elements have been removed okay so
similarly or something called insert
okay so insert what it does is in the
you can you add the element at the
second index so in the insert the first
parameter is basically the index and the
second parameter is the value so when
you say to nine so at the second index
element man is going to be inserted and
that was your questions universal say
you were asking me that how would I like
to remove the third element so that's
how you use a removed parameter okay
similarly if you say insert and you give
to and then followed by a list so
basically this inserts you know all
these numbers in the second index
similarly if you say remove for two so
here two is the index so it removes an
element from the second index and it
also has remove another overloaded
operator where you can specify the index
and also how many elements you want it
to be removed so you can say that I know
you can just take the list and you know
from the second index remove three
elements okay so there are a lot of
utility methods here so I suggest that
you can you take a look at them okay
indulge it I haven't gone to that so
just huh so any any questions on the
common operation so I suggest you know
you have a look at this color docs and
go through it okay now let's look at
some transformation I've already shown
you the transformations here so you know
the thing is that you know you we
declare
so you remember decided we had here so
that that couple of more elements so
this is the area we have now okay and
now you know if I want to print
gentleman on the ice or I can do like
this okay
or I can do like this as well okay so I
can say the number I can see a RR and
then I can see printer lint
I can do this is a but this is more
preferred okay so in production I
suggest you do this this is not visible
this is not how you do it this is the
way recommended way of doing
in case you want to just print out the
odd numbers so now you just want to
check the odd numbers again you can give
the guard condition what I taught you
yesterday okay so you can say if in a N
what if you do not equal to zero so you
can just drink the odd numbers here okay
so that's exactly what this example is
doing now the thing is if you want to
collect you know the numbers then you
can use ield okay so so there's another
way of doing it but you know I won't
teach you these things because this
actually you won't be doing it like this
you know you know if you want to extract
order even numbers from from a list this
is not how you code okay this is very
silly way of doing it into color ideally
in practical cases and you'll be using
filter functions you know I'm going to
teach you all these things in the next
module so so ideally you will do like
this
okay so so you will actually write code
like this okay instead of code like this
that's not how you do it okay this this
is actual color in doing it but don't
worry about it and are these things I'll
be teaching in the next module filter
are produced and other other utility
functions okay good so so that's about
you know area buffers now let's go to
other common operations you know it has
in a utility methods like some max so
you can you can actually generally you
know get a summary so here the air are
so you can call the error code sound it
gives you the sum of the collection then
call max sorry you can call max which is
the max number and the VIN number okay
so all these things automatically
available to any numerical action you
can use them okay now let's look at maps
so masa like you know hash tables so
they're like key value pairs so in color
a map is a collection of you know pairs
key value pairs so I'm sure you've used
inner hash tables or match in your
career
they are you know by adding in the
initial program these are needed and the
pair has you know two values done
naturally at the same time okay so let's
let's declare a map okay so
the thing is madame equals to map so
here you specify the key to say for
example I am specifying the roll numbers
and the name of students so so here what
I did was in I declare the map and here
is the key okay the key is 1 so
basically the key can be any data type
okay so here it's integer so which is
which may be the roll number of the
students
kind of values the name and you give an
arrow here so it's sent accesskey arrow
value and it can be of any data type so
I created a map basically where the key
is integer and the value is string okay
and this is what my map is and it's an
immutable map okay so that means you
cannot change the map okay you you won't
be able to do you won't be able to
change the map so the thing is that say
for example you know you want to you
know delete you know chutki you won't be
able to do that today because it says
it's an immutable map so if you want to
create a mutable map so this is how you
do it so you do an import scholar drop
collection dot mutable dot map okay and
then you are going to use this map here
so now it becomes a mutable map okay so
there are two map classes you know in in
color there is a mutable and there is an
immutable okay and every collection
becomes a spares
so there is a mutable collection an
immutable collection okay so there is a
map here and if you see the map here so
there is an immutable map here in the
immutable package
similarly there is immutable members so
they come in pairs you know mutable and
immutable and you can use the one which
you want
so now what I've done is and I have
created a mutable map of Jenny and Benny
and this is the map I have and if you
want to access the elements of the map
so you can do like this so you can say m
and you can give the key it prints penny
and if you give em - it prints Jenny and
if you give some rubbish which has some
key which doesn't exist still give you
or tons of errors and I'm saying that
key not found so there's another way of
doing it so you can call em door get in
a one-state basically returns as an
option so you won't be learning options
in this course it's a pretty advanced
concept but just remember that you know
there's a method called get in which
returns the value
another utility method I'm telling you
the important methods which you'll be
using in the map so it's called get
orange okay so what it'll do is it will
try to look for the key and the key is
missing then either you can give an
alternate message like you know key not
thought okay so here obviously one is
existing so it says Lenny would say for
example if you use 100 so then it is key
not font okay and you can give any
message here you know sorry any messages
okay so you can see data missing okay or
you can actually give minus hundred of
anything you want okay you can do
anything you want here so that's
basically an important method okay now
you cannot put multiple keys or a file
at so you can only put a single key
there okay and and if you want to delete
keys so if you do like this so you can
give the King name so then it's added
okay and if you want to add a key so
then you can again say
you know add the key back so now this
hour and in the key back okay
so no I was just waiting for Shelly's I
was just waiting for Venkata to ask the
question he has a question okay banker
is asking me that can we use get orals
without a key
no ven could it really doesn't make
sense because when you are trying to get
something you can only get from a map
based on some you know based on some key
okay so if you don't have the key that
how are you going to get it got it so
now you cannot do that benkard so when
you when you mention when you use a get
Orleans API you have to you have to use
know the key so let's look at the
documentation you know so that you don't
have any doubts so if you go to get
Orioles she would have better get our
heads okay so the signature clearly says
that you know you you give the key here
okay so you have the key here and and
also you give the default okay so if the
keys in case not found then the
computation it clearly says that in a
computation that ins a default case in
case no key is found okay there's a
couple of interesting questions one
question from row he's asking it in Val
and we're in a really makes any it
doesn't make any makes any difference
until we really import our mutable and
immutable collection see the thing is
that in a you to understand the
difference between mutable and immutable
collections and Vallon back so when you
actually declare them as bad so that
means the references can be changed okay
when you declare them as mutable when
you import them as mutable or immutable
that means the values can be changed
okay so if you use a mutable map that
means the values inside the map can be
changed but if you but you can still
make that as a bad okay as I'm doing
here so so here you see that you know I
have declared a map you know it's a
mutable map so that means I can change
the values but I can't change the
reference because I cleared it as well
okay so so there's a distinction between
a bell that as well as and on the other
hand mutable and immutable pura so I'm
glad you asked this question so mutable
basically makes it you know whether you
can add inner values you know to the
collection or not and battlin bar
basically differentials whether you can
change the reference or not I can type
clear all of you so just remember that
you know okay we have one more question
from Ganesh that's also very interesting
question Ganesh is saying that how do i
instead between keys so so suppose there
is a key one here okay so there's a key
one and the key to as in this case you
know Benny and Jenny to students Ganesh
is asking me that and how can I insert
in something in between now I would like
to ask you you know I just like to put
the question back to you and ask you
whether it's really possible so is it
possible to remove elements from a sorry
is it possible to do this kind of
operation at or what do you think okay
well done Praveen world and universe so
I think you gotta try it
see the thing is in a couple of things
you have to get in place okay the thing
is firstly when you talk about the hash
tables okay so I just mentioned what I
am doing when you talk about the hash
tables on a map okay it's basically on
this in computer science okay it's
always unordered okay so it is never
ordered solid unordered that means it's
on soccer and white is unsorted because
if you look at the functioning of a hash
table they use something or the hash
function you know to determine you know
the location of the key and value okay
so where actually your key value pair is
going to be stored in the data structure
you really don't know you don't have any
clue on that that's if you get them in
by the hash function so it's what ball
so left key one is here key one is
somewhere here and key one is somewhere
here
key 2 can be here and I have to give one
there can be key hundred okay so the
order definitely we don't know what is
the order it will depends on how the
hashing is done okay so I won't get into
the details but just remember that in
hash tables map they're always unordered
and so obviously if that's the case then
really it doesn't make sense to insert
between keys or before keys because the
ordering there doesn't matter you know
it's it's purely random access clear
Ganesh okay so Allah is asking that can
we remove elements from any mutable map
okay what is the definition of immutable
immutable map basically means that you
cannot change the map you cannot change
the elements of the map once it has been
in a once it has been created so that's
the case then obviously we won't be able
to change it now let me ask you a couple
of more questions okay now that we are
just a minute let me see anything else
is there in the map no writing out only
everything about math
before I go to the next stop a couple of
things I want to ask you okay this is
related to programming and you will be
using this a lot when you're doing it
some serious color programming is that
when you know should you use
mutable versus immutable collections is
not only map you know it can be it can
be anything like Arab array or sorry
buffer or list or vector anything
so when should you do that the thing is
if I just remember this that if you're
writing an APA say for example you know
if you if you're writing a function say
you know get customer records okay and
this is maybe you marathon you know
talented collection that immutable map
you know you can you can have the
customer ID which you know which can be
an integer and you can have you know the
customer itself
the customer object okay so so you can
actually create something like this okay
I just hope
and so that you know what are the data
rate so basically you have in a
something like a map like this okay
happens is not NAU you are sending an
immutable map with customer IDs and the
customer objects now here the advantage
of this kind of an API is that you know
when you send it to the user the user
won't be able to change in any records
so it's more like a constant thing which
he gets an e cannot only query and
figure out who is doing what rather than
so you know rather than changing stuff
okay so so when you're designing ApS
which are tons in values to people so
it's a good choice to make it immutable
so if you are sending in the form for
collection weather then that makes it
more robust and flexible and you don't
have to worry about any mutation and the
client-side okay yes you're right Rafael
a sort of fella saying that they may use
mutable if you are intending to change
the contents and immutable if the
contents are not expected to change your
arrogant revilers so that's exactly what
I what I explained now shall Ajay saying
that when you know the elements might
change for example the orders of
customer and then you can go for mutable
but customer name can be immutable
absolutely right so these are the
examples you know various examples I'm
glad in all of you really internalize
this and even Carl is saying that you
should use immutable collections when it
is fixed so so typically the thing is
you know you should go for in immutable
types when you're returning data to the
client and the client can only take the
data and maybe show it in a web page or
do some processing with that in that
case you know you don't have any fear
that your data can get corrupted or
changed by the customer okay so that's
that's the advantage of this there's an
L so that's one advantage okay so that's
one advantage of a mutable immutable so
basically it's data integrity okay
that's one at what is the second in
their advantage which surprisingly no
one said
there's actually synchronization okay so
synchronization overhead is reduced see
the thing is that you know we why do we
synchronize we synchronize because it's
quite possible that you know two threads
can change the state you know awful
awful data of an object so we need to
synchronize to make sure that one only
one thread you know and read the object
at a time but the thing is that either
the data is read-only so if you have a
read-only data so it there it really
doesn't matter to synchronize okay so
because it's read-only so no matter good
friends read or you know 300 threads
read that particular data the
cannot be changed by anyone so you don't
need to synchronize with this everybody
is going to read the same stuff it's
just like the newspaper ten people
reading the newspaper you don't have to
synchronize because nobody can change
the news okay so it's just printed and
whatever is printed people read here are
looking so just remember that you know
the utility of that's basically the use
of immutable
so what's the data integrity and second
is the segmentation overhead is
minimized
clear all of you any any questions on
this one ever hears canister right for
the nation saying that we are using
mutable as less as possible exactly I
mean we don't use mutable much unless
you really have a good use case to do it
okay so now we come to the next data
structure called doubles so apples
actually in time more practical
scenarios in it you won't be using
couples a lot because there's something
called case classes in color so we'll be
using the case classes a lot instead of
tablets let us go to know what apples
are and but for all practical purpose we
won't be using tuples but okay so double
the modulus forms I know because we saw
that you know any restoring things in a
list
you can only store in a homogeneous
inner entities you cannot you won't be
able to store a tree any stuff but in
Chapel W Jinnah you can store more than
two values or potentially different
types okay so that's the advantage and
these are pretty useless you know in
most of the practical cases because we
use something called case classes in
Scala
just to you know just to visualize this
is to understand so say for example in
you are reading in a table you're
leading a row from a database table so
it can have an employee name and
employee ID and employee address so that
is impossible you read that in a double
ok so so let's understand you know this
particular thing
for example we I declare double Val D
curve so I can I can write like you know
say the employee ID 100 employee name is
a John and the address is you know
anyway say you know crunch so now I've
created a couple of integer string and
string and if you want to access the
tupple this is how you do it so it's
always you give it underscore first you
have to give a dot and then you have to
give it underscore and the index doesn't
start from one it's that sorry it
doesn't start from zero it starts from
one so it's a funny way of accessing and
they do not know whiny and this is how
it's done so underscore one gives the
first element and underscore two gives
second an underscore three is the third
element okay
and typically the use cases are say for
example you're reading a table from a
database and as and when you read the
rows you know you can keep the rows in a
double and and then you can process so
basically you can either you can create
in a row of you know a collection of
tuples and then turn it across but
usually you know what I have seen and
obviously if you can do operations like
instead of 100 you can make it 200
and obviously you cannot do 200 because
you have to give this T as well so if
you make this D as in a wire then you'll
be able to you know and you'll be able
to sorry what happened oh sorry
nothing is when you when you create a
couple the reference can be changed but
in the values are constant so you cannot
change couples that's why definition so
that means you know once the value has
been assigned you cannot you won't be
able to change the values of the double
it's very similar to Python tuples and
in right and also you know once you
create a dropper you won't be able to
change it so here it's also the same
thing
one thing is what you can do is these
are very useful you know for sending
data across across processes or across
you know across boundaries I hope you
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