#11.1 Kotlin Tutorial: "filter" and "map" Using Lambdas for Filtering and Sorting Collections PART-1 Video Lecture | Kotlin Tutorial for Beginners: Learn Kotlin in easy language - Back-End Programming

hi resisting Siddarth once again welcome
to the next module of this cortland
programming series now in the previous
two modules we learnt about the lambdas
high-level functions and collections now
what are the practical usage of lambdas
and high-level functions as well as
collection how can we use all these
three together let's check it out in
this module so with the help of
filtering and sorting we will check out
how can we use the lambdas and
high-level functions inside the
collections so in this module let us
check out what are the topics that we
will cover so first we will check out
the various important functions such as
filter and map now these are the two
very important methods that are
frequently used with collections and
lambdas and now proceeding forward we
will check out what are predicates in
Kotlin now a predicate in short is just
a condition that returns true or false
so inside the predicate we will check
out all any count and also find
predicates now at the end we will check
out few more functions such as a flat
map and also distinct so this module
will basically cover all the operations
that you can perform on the collections
along with lambdas now in this video let
us check out what our filter and map in
case of Kotlin so first of all let's
check out what is the filter now the
filter method actually filters out the
desired results from a particular
collection or list so if you want some
elements based on some condition then
you can simply use filter to get the
desired elements from a particular list
now similarly we have map function now
suppose you want to perform some
operation on some desired elements so
you can use map method and simply
perform some operation and also you can
modify the elements so this map will
simply return the elements in the
modified form so inside the IntelliJ IDE
at the top I simply define the
definition of the filter and also map
right now inside the main method I
simply defined the list of numbers now
this is actually the immutable list that
is you cannot modify it later
so the type of my numbers will be list
of integer values right now down the
side let us perform some operation on
this list of numbers and get the desired
results such as let us separate out the
small numbers my small numbers equal to
use my numbers here and now use the dot
operator followed by filter method now
if you notice here this filter method is
actually expecting a lambda as a first
parameter so you can simply define a
lambda now this lambda here it shows a
predicate now the predicate is actually
a condition that simply returns a
boolean value so in our case it will
simply take integer as a value and
simply return the boolean value either
true or false
so if the condition is true it will
simply return a particular element and
store it inside our new list right so
here I will simply use filter followed
by the lambda function so here curly
bracket open and close so inside this
let us define our lambda so here I will
simply define my let's say variable V
goes to let's say V smaller than 10 so
this statement will simply return a new
list containing all the elements whose
values are smaller than 10 so in our
case we have 2 3 4 and 6 so these are
the four elements who that are smaller
than 10 right so down the side I will
simply print out the value by using the
for loop so this is the for loop to
print out the values so let us now run
the code so here we get 2 3 4 and 6 in a
new list so this filter method actually
returns a new list containing the
numbers that satisfy this condition V is
smaller than 10 right so this is
actually the predicate right now instead
of using V going into V smaller than 10
here we have just one parameter so it
can be replaced by I T that is it it's
smaller than 10 so instead of using V
going into V
more than 10 you can simply write it
smaller than 10 so here let me write the
comment line right so either of these
two you can write here it's smaller than
10 or we going into V smaller than 10
now this V can be num as well it is
totally up to your wish because it is a
variable name right now down the side
let us now explore the map now the map
actually returns a list containing the
results of the applying transform so
when we are using the map suppose I want
to get the square of all these numbers
so for that what I will do I will simply
use the map method that simply expects a
lambda as a parameter like we have in
case of filter so down the side let us
use Val my squared numbers equal to my
numbers that is our original list dot
map right now here again you can notice
the map actually expects a lambda now
here we have a transform so what
transformation that you want to apply on
the current list that is my numbers so
for that what I will do I will simply
define the lambda function inside which
I will simply write let's say numb going
into numb into numb right so this is a
parameter and this is actually the value
that we are getting inside the list so
for each element this is actually
applicable so when this code will be
executed we will get to square 3 square
4 square and so on till 90 square now
instead of this you can also use it
operator or the keyword it as strict it
because we are just having one parameter
of num so this is actually the
alternative to that so here let me write
the comment lines so booths are actually
same right now let us now print the
result by using the for loop so simply
copy this for loop and down the side let
us print the values by simply changing
the list by my squared number 8
now let us run the code so here in the
output console for the second loop we
have the output as 4 9 16 36 5 2 9 and 8
1 0 0 so these are actually the squared
form of our original list this one and
this is the output of the previous 4
loop so please do not confuse about it
now if you notice the variable of my
small numbers and also my squared nums
let us check out what is the data type
of this so simply press alt enter and
specify type explicitly so here we get
list of integer values right so this
filter function simply returns the list
of integer values that satisfy this
condition so whatever so all the numbers
that satisfy it smaller than 10 will be
stored inside this list now similarly
here here this map function simply
returns the transformed data that is the
square of all the numbers and store it
inside my squared nums now proceeding
forward in Kotlin we can use the filter
function and also the map function all
together now suppose you want to filter
out some data and then you want to find
the square of all the numbers so for
that you can simply define a new list
let's say my small squared numbs equal
to my numbers that is the original list
dot predator so here let us define let
us copy this lambda and paste it here
and then you can simply use the dot
operator dot map and then find it as
trick it right now here let me commit
these two for loops so as to get the
better output and now let us use the for
loop here to print out the result so
here what we're actually doing is when
this statement will be executed
we are simply filtering out all the data
that satisfy this condition it's smaller
than 10 right and then on the filtered
result we are simply applying the
formation that is we are simply finding
out the square of numbers now for this
let us format our codes to make our code
more cleaner so dot filter and then
apply dot map method let us now run the
code so here in the output console we
get the square of all the numbers that
are smaller than ten so we are getting
the square of two three four and six
twenty three and ninety are actually
excluded at this step right so after
this step we are applying the square of
the numbers available so this was all
about the filter and map now let me give
you one more example so for this I will
simply define a class of person so here
I have a class of person that simply has
the property of age and name right so
inside the main method I will simply
write some code in order to make your
concept more clear so I will simply
define the list of person so here I have
two objects person person of the age of
ten and name Schrank
person of the age of 23 and named Annie
now let us define one more person and
give the age as let's say 17 and name as
let us say Sam right now on the left
hand side let us assign it to let us
save people list of person equal to
people now this people is actually of
the type of list of person right so no
doubt till noun so even if you remove it
then also our code will work perfectly
fine now down the side how can we apply
the filter and also map on this people
list so now suppose from this list of
person I just want to print out all the
names that is stored inside the people
list so for that I will simply use let's
say people dot map so here I will simply
use let's say person P going into let's
say P dot name right now since this is
only one parameter here so we can simply
replace it by it so no doubt till now
and again assign it to some let's say
names equal to people dot map so this
map method will simply apply
transformation and simply return all the
names present inside the people that is
shrink Annie and Sam will be stored
inside the names let us now print the
names so here is the for loop for that
so let us now run the code so here we go
in the output console we get shrink
Annie and Sam and now suppose you want
the list of names along with you want
only the names that starts with s right
so for that again you have to use dot
filter operator so what I will do is I
will simply use dot filter that simply
expects a lambda so for that I will
simply use person going into person dot
name dot starts with and here I will
simply pass capital s now again since we
have only one parameter here so it can
be replaced by it I T and now let us run
the code so here we go in the output
console we have shrink and Sam we don't
have any here because Annie starts with
a and we just want to filter out the
results that starts with s right so here
let me format the code as well so as to
make our code look more cleaner so dot
filter and then apply dot map so this
was all about the filter method and also
the map method now remember these are
the most important methods that we will
be using in our upcoming videos as well
so as of now thanks for watching and
have a good day thank you