Part 73 What is dictionary in c# continued Video Lecture - C sharp Enhance

this part 73 of c-sharp tutorial in this
video we'll discuss using dictionary
object in c-sharp this is continuation
to part 72 so please watch about 72
before proceeding with this video in
this video we'll discuss these four
methods try get value count remove and
clear
we'll also discuss using link extension
methods with dictionary and finally
we'll look at different ways to convert
an array into a dictionary let's flip to
visual studio we'll be using the same
example that we started in part 72 so
here we have a customer class with three
auto implemented properties and in the
main method we are creating three
instances of that customer class and
then we created a dictionary and we
added these customer objects as values
within the dictionary and the respect to
customer IDs as keys now let's look at
using this try get value function first
of all when do we use this function if
you're not sure if the dictionary
contains a specific key that's when we
use this function and what does this try
get value function returns as the name
States it's going to return a value that
is associated with a key there are
several ways to do that in the previous
session you know we discussed one of the
ways to get a value that is associated
with a specific key is by you saying you
know something like this so look at this
when we pass this key 1 0 1 you know
what is it going to return it's going to
retain a customer object because this
dictionary contains I mean the value
within this dictionary is a customer so
we get a customer back this is one way
but then if I use this approach and if
that key doesn't exist within the
dictionary then we are going to get an
exception so if you're not sure you know
if the dictionary contains a specific
key and if that key doesn't exist if you
don't want to get an exception then use
try get value so let's see using try get
value function if you notice this try
get value function it expects two
parameters the first parameter is the
key okay so I want to get the value for
this case so that's going to be the
first parameter and if that key is
you know the second parameter look at
the parameter type its customer okay
because the value within the bit in this
dictionary is customer okay so the type
is customer here so whatever parameter
that we are going to pass here is going
to receive the value that is associated
with that key okay and notice that it's
an output parameter okay because we are
going to get the value back we are not
going to give it a value but we are
going to get to get a value so let's go
ahead and create a an object reference
variable of type customer and then let's
pass it as a second parameter so this
reference variable is going to receive
the value that is associated with that
key and since this is an output
parameter we have to have out keyword in
front of that okay and notice the return
type of this function from the
intellisense what is it returning it's
returning a boolean meaning it true or
false if there is a key 1:01 within the
dictionary then this method is going to
return true okay since the return type
is boolean we can use this in an if
condition okay so if this key is found
this function is going to return true
and this parameter is going to receive
the value that is associated with that
key in that case we want to print the
details associated with that customer so
I want to print their ID their name
and their salary
so where are we going to get the idea
from from the customer object so
customer ID customer dot name and
customer dot salary all right now if
this key doesn't exist in the dictionary
then what's going to happen this
function will return false and this
parameter will be now okay so in that
case we want to print a message stating
the key does not exist within the
dictionary maybe the key is not found
all right now do we have an item with
that key within the dictionary yes we do
in fact the first object has got ID one
zero one so let's go ahead and run this
and see if we get the output that we
expect okay look at that we have the
details of that customer okay now on the
other hand if I pass something like one
one one we don't have an item with that
key so it should come to the else block
and say that T is not fun but the
important thing to keep in mind here is
we don't get an exception all right now
let's look at using this count function
first of all when do we use this
function now as the name States if you
want to find the total count of all the
items that is present within the
dictionary then we use that count
function actually there are two ways to
find the total number of elements that
are present in a dictionary one has to
use the count of property so this
dictionary class exposes a property
count property and look at the return
type at Synthesia so it's going to
return the total number of items within
the dictionary so let's say we want to
print something like total items equals
so now as you might expect when we run
this we should get to the light on
sequel 3 so here we are using this count
property and this is defined within the
dictionary class itself now instead of
using count property I can also use
count function okay
now when is this count function present
it's actually present in a different
namespace so if I right-click on that
and if I go to the definition look at
that this is first of all an extension
method look at that it's a static method
and the first parameter is of type this
and this which should be present in a
static class so this is definitely an
extension method on ienumerable class
and look at the namespace its present in
system dot line meaning this is a link
extension method so we are using a link
extension method on a dictionary object
so when we run this we should get the
same output total items equals 3 now
there are two overloaded versions of
this count function the one that we have
just used you know doesn't take any
parameters but there is the second
overloaded version where we can specify
a predicate okay and let's say for
example I want to find the total count
of employees where the salary of the
employees is greater than 4000 okay now
if you look at the customers that we
have here there are two employees whose
salary is greater than 4000 customer 1
and customer 2 so I want to find the
count of all such employees and we can
very easily achieve that using this
count function okay now look at this we
are using an extension method on this
dictionary and then we are going to pass
a predicate here okay now since we are
using this count function on a
dictionary you know when I say key value
pair here so key value pair such that
key value pair dot so basically what we
are doing is we are passing you know
this predicate here okay so what I want
to do is we are using this count
function on this dictionary so we are
going to get a key value pair access to
the key value pair
that is present within the dictionary
object and we want to find the value so
what is value value is nothing but the
customer object itself so and then this
value will have all the properties of
the customer so ID name salary because
this value itself is nothing but a
customer object now what we want to do
is you know key value pairs such that
key value pair dot value dot salary
should be greater than 4000 so if this
condition evaluates to true then that
employee will be included in the count
otherwise he will be excluded so when we
run this we should get the total count
as two because we have only two
employees whose salary is greater than
4000 similarly you can include any
condition you want maybe you know I want
the count of all employees whose name
starts with maybe letter s you know you
can give any condition so any expression
that you give here should have to
evaluate to true you know if that has to
be included in the count if it evaluates
to false then it will be excluded from
the count all right
now let's discuss using remove function
so anytime you want to remove an item
from a dictionary then you use remove
function so obviously let's say at the
moment this dictionary has got you know
three items and let's say I want to
remove an item which has caught this key
one one zero and to do that they simply
say Dictionary customers dot remove and
then you specify the key of the item so
one one zero should remove that from the
dictionary okay
what is going to happen if I specify a
key that does not exist basically if the
item with that key doesn't exist then
you wouldn't get an exception and
nothing happens so that's fine all right
so the next function that we discuss is
clear now if you want to remove all
items from the dictionary so remove will
remove one item from the dictionary but
if you want to remove all items from the
dictionary then you use clear so when
you use clear look at the intelligence
it states remove all keys and value
from the dictionary so it's going to
remove everything okay and then we have
seen using link extension methods with
dictionary and finally let's look at the
different ways to convert an array into
dictionary now at the moment we have you
know we can get rid of this dictionary
so at the moment we have created three
customer objects here now let's create a
customer array so customer and let's
call this maybe customers equals new
customer array and I want to whole let's
say three elements within that array
okay so we can basically say customers
of 0 equals customer 1 and similarly
within the first location going to store
customer
and then here maybe customer three okay
now we have an array here now can we
convert an array into a dictionary
absolutely all you need to do is on that
object so customers dot - dictionary
look at that you have this - dictionary
method so simply call this - dictionary
method and then obviously when you want
to convert an array into a dictionary or
let's say for example when you want to
create a dictionary there are two things
that you need to specify what is the key
for the dictionary and what is the value
okay so obviously when we are converting
an array into a dictionary we need to
specify that as well so all the objects
that I have in this array I want to
convert them into a dictionary type okay
so here the customer objects is stored
in an array but I want now to store them
in a dictionary and obviously when if we
want to create a dictionary we need to
specify the key and the value
okay now so here I'm saying so each
employee or customer such that the ID is
going to be I mean the key is going to
be ID of the customer and then I am
saying value is going to be customer
okay so here basically what we are
saying is the key is going to be
customer ID and the value is going to be
customer object itself okay so now let's
actually look through let's so this -
dictionary is going to return a
dictionary bag
so let's store that in a dictionary so
the key is going to be integer and the
value is going to be of type customer
and let's call this maybe dictionary
okay now let's say if we have caught all
the items within that dictionary and to
verify that let's use a for each loop so
for each so what's the dictionary again
dictionary is a collection of key value
pairs so we are going to say for each
key value pair integer and customer and
let's call it kbp
in our dictionary so in this dictionary
now we are going to have the customer ID
as the key and a customer object itself
as the value okay and we are looping
through each item within the dictionary
so let's say console dot readline we
want to print the key and values so key
equals and how do we get the key from
this variable kbp what key should give
us that and then obviously value within
the dictionary is a customer object so
let's create a customer object and maybe
let's call this first equals k vp dot
value should return a customer object
back and then maybe we want to print
their ID name and salary so ID equals a
placeholder there
so first direct ID last name and finally
past dot salary so now let's run this
and look at that we get the output so
it's very easy to convert an array into
a dictionary not only array you can even
convert a list of customers okay let's
say for example instead of this
customers array I have a list of
customers so let's create a list of
customer
and then obviously to add items to the
list we use add method so let's call it
customers dot ad and let's make a copy
of this so we want to add customer one
object customer to object and customer
three object
now this customers is actually a list
but we are using essentially the same
syntax to convert the list to a
dictionary so if I go ahead and run this
now we should get the same output all
right that's it for today thank you for
listening have a great day