Back-End Programming Exam > Back-End Programming Videos > C sharp: Enhance your Skills (English) > Part 72 What is dictionary in c#
Part 72 What is dictionary in c# Video Lecture - C sharp Enhance your Skills
Text Transcript from Video
this is part 72 of c-sharp tutorial in
this video we'll discuss dictionary
object in c-sharp a dictionary is a
collection of key-value pairs so when we
create a dictionary we need to specify
the type for key and value and this
dictionary class is present in systems
or collections but generic namespace and
the fastest way to find a value within
the dictionary is by using its key and
keys within the dictionary must be
unique let's understand this dictionary
with an example let's flip to visual
studio so here I have a console
application we'll be making use of a
customer class in this demo so here we
have a customer class with three auto
implemented properties first of all
let's go ahead and create some customer
objects so let's call this maybe
customer one equals new customer and
then let's initialize the properties
let's say ID equals one zero one maybe
name equals mark and salary equals five
thousand and let's create two other
customer objects so let's make a copy of
this customer object and let's change
the object name to customer date to and
here customer three and let's set ID to
maybe 110 Pam and maybe something like
six thousand five hundred and similarly
let's set this to maybe one nineteen is
the customer ID John is the name of the
customer and maybe his salary is three
thousand five hundred
okay now let's go ahead and create a
customer dictionary first of all this
dictionary class is present in system
that collection store generic namespace
so let's go ahead and bring that in
alright now when we create a dictionary
we need to specify the data type for its
key and value so basically remember a
dictionary is a collection of key value
pairs
okay so let's create a dictionary and
look at this the moment I open this
angular bracket in
it asks for the type for the key and the
type for the value so we are going to
create a customer's dictionary and the
key for this dictionary is going to be
the ID of the customer and the value is
going to be the customer object itself
okay so the key is going to be integer
because we want our key to be customer
ID and customer read IDs of type integer
and the value is going to be the
customer object itself so that pipe is
going to be customer and let's give this
dictionary a meaningful name let's call
this dictionary
maybe customers so we have just created
a customer's dictionary the type for the
key is integer and the value and I mean
the type for the value is customer ok
now let's add these customer objects
tour dictionary all right and to add
items to the dictionary we use add
method ok and look at this the moment I
open the bracket it prompts me the key
has to be integer and the value has to
be customer object so where do I get
customer one's ID from using the
customer one object so customer 1 dot ID
is going to give us the idea of customer
1 which is an integer type and we want
to store the object itself customer one
object and similarly let's go ahead and
store customer two and customer three
all right so at this point we have
created a dictionary and we added
customer objects to the dictionary okay
now we want to find customers within
this dictionary and the best way to find
a value within the dictionary is by
using its key what's the key here the ID
of the customer now let's say I want to
find the details of this customer who
has caught this ID 1 1 9 so the fastest
way to retrieve this customer object
from this dictionary is to use the key
for that dictionary the key here is
customer ID which is 1 1 9 so look at
this the moment I say dictionary of
customers open a square bracket look at
that it prompts me to enter the key ok
what is the key its customer ID of type
integer so we want the details of
customer 1 1 9 so I simply pass their ID
and look at what it is returning back
it's returning a customer object back so
let's do that in a variable of type
customer and maybe let's call this
customer 1 1 9 ok so we have just
retrieved a value from the dictionary
using its key alright now if I want to
print the details of this customer we
can simply use console dot readline
let's say I want to print the ID and I
also want to print name and then salary
as well
okay so where are we going to get the ID
from from this customer object so
customer one 19.8 a bear named and
finally their salary all right so let's
run this and see if we get the details
of customer whose ID is one one nine
there we go
the details match all right okay
so is it possible to loop through each
item within the dictionary absolutely
now if we have a list of customers for
example then we can loop through each
item within that list of customers using
a for each loop similarly here I have a
dictionary of customers so is it
possible to loop through each item
within that dictionary absolutely okay
so let's use a for each loop let's get
rid of this line right here so for eat
now if you have a list of customers then
you know that list is a collection of
customer objects but here this
dictionary is not as simple as saying
this dictionary is a collection of
customers it's actually a collection of
customers and their IDs so here we have
the key and a value okay so a dictionary
is a collection of key value pairs so
here when we loop through we have to use
key value pair because a dictionary
session Chile a collection of key value
pair of objects and when we use key
value pair we need to specify the type
of the key and the type of the value the
type of the key is customer ID which is
integer and the type of the value is
customer object itself and give this a
meaningful name and maybe let's call it
customer key value pair n dictionary
customers
okay now to get the key up from the key
value pair all you need to do is
customer key value pair dot key and look
at that what is it returning it is it is
returning an integer back nothing but
the ID of the customer so let's say we
want to print the ID console dot write
line ID equals so that should print the
ID now what is the value within this key
value pair it's nothing but the customer
object itself so look at this the moment
we say customer key value pair dot value
and look at the intelligence what is it
returning back it's returning a customer
object back so let's store that in a
variable of type customer maybe let's
call it cost all right now if we want to
get the old values out of this customer
object we can very easily do that using
the respective properties ID name and
salary so maybe let's go ahead and print
the ID name and salary so again to do
that ID equals maybe a placeholder there
similarly name equals and salary equals
all right so cost dot ID and similarly
customer dot name and customer dot
salary so when we run this as you might
expect it should loop through each
customer and then pull out there
probably let's call this key because we
are actually pulling out the key so we
know that's the key and this one is the
value and then maybe let's include a
dotted line here so that each customer
will be separated
all right so let's go ahead and run this
now it should loop through each customer
and print the values look at that we
have customer whose key is 1 0 1 1 10 1
19 and their respective details so you
can find you know values with an a'
dictionary either by using the key like
this which is the fastest way basically
to retrieve an item from the dictionary
or you can loop through each item within
the dictionary ok and keep in mind a
dictionary is a collection of key value
pairs
ok now here we are using a key value
pair now instead of using key value pair
we can also use an implicitly type 2
variable something like this wire ok now
if I run this it's still going to work
the same way let's go ahead and close
these windows here let me run this once
again look at that I have the same
output instead I mean the only change
here is we have changed you know the
datatype to where the implicitly typed
variable now it should be used this one
or should we use key value pair my
personal preference to use key value
pair because that way your code is more
readable rather than using this
implicitly typed variable because just
by looking at this code right now here I
can't tell what is the type of the key
and what is the type of value on the
other hand if you use key value pair
then you know you know what is the type
of the key and what is the type of the
value okay so your code is more readable
so as far as possible try avoid using
this ver keyword which is an implicitly
typed variable all right now is it
possible just to loop through the keys
within the dictionary absolutely if you
want to just get keys let's actually
comment this line so I want to loop
through you know through all the keys
within the dictionary if you want to do
that so dictionary object has got keys
property so which is going to return the
list of keys back now what are our key I
mean what is the data type of our key
it's nothing but an integer so we are
going to get an integer back
okay so let's call this maybe key and
then let's say console dot write line D
key so it should print out all the keys
now so let me go ahead and run this and
look at that we have all the keys
similarly is it possible to retrieve
only the values that are there within
the dictionary absolutely so instead of
using dot keys property all you need to
do is use dot values property but what
is value type it's nothing but a
customer which means we are going to get
a customer bag so let's call this maybe
customer and let's say cost is the name
of the reference variable let's get rid
of this one
let's uncomment this line so if you look
at this piece of code it's
straightforward all we are doing is we
are retrieving the ID name and salary
from that customer object so let's go
ahead and run this now and look at that
you get their values as expected all
right now another thing to keep in mind
is the keys within the dictionary must
be unique so if you look at this
dictionary this customers dictionary we
already have used these three keys one
zero one one ten and one nineteen so
what happens if I try to add let's get
rid of this code so what's going to
happen if I try to add maybe customer
one object once again when I build this
do I get a compile error no build
succeeded but then I plan this we kept a
runtime exception look at that
argument exception an item with the same
key has already been added so we already
have a key with the same I mean the same
key within the dictionary so we have
that exception so keys within the
dictionary must be unique when you try
to add them make sure you know the keys
the key doesn't already exist so how to
check if a key exists or not
again this dictionary object has a class
method called contains key okay so you
can specify the key that you want to add
there you can pass it as a parameter so
if that dictionary doesn't contain that
key then go ahead and add this so if
you're not sure whether the key is
present within a dictionary or not you
can use this contains key method it
returns a boolean a true or false so let
me run this now look at that we don't
get any error right now because this
piece of code wouldn't be executed
because the key is already there so this
line will be skipped not only while
adding even when you retrieve the values
from the dictionary using keys
make sure the dictionary
it has got the key before you try to
retrieve a value look at this when I say
customer maybe cost equals dictionary
customers and then let's say I want to
retrieve a customer object whose ID is
maybe 135 now that's this dictionary
contain a value with that ID no it
doesn't so what happens when I try to
build the solution look at this bill
succeeded we don't get any compiler
error but when I actually run this we
get an exception at runtime key not
found it exception so basically you try
to look up a key that doesn't exist so
you use this key that doesn't exist and
that's why we have that exception so
again check if the key exists or not how
do you do that the same idea so
dictionary customers dot contains key
whatever key that you are trying to look
up so if that key is present only then
execute this piece of code there are
several other useful functions within
this dictionary class we'll discuss them
in our next video session that's it for
today thank you for listening have a
great day
this video we'll discuss dictionary
object in c-sharp a dictionary is a
collection of key-value pairs so when we
create a dictionary we need to specify
the type for key and value and this
dictionary class is present in systems
or collections but generic namespace and
the fastest way to find a value within
the dictionary is by using its key and
keys within the dictionary must be
unique let's understand this dictionary
with an example let's flip to visual
studio so here I have a console
application we'll be making use of a
customer class in this demo so here we
have a customer class with three auto
implemented properties first of all
let's go ahead and create some customer
objects so let's call this maybe
customer one equals new customer and
then let's initialize the properties
let's say ID equals one zero one maybe
name equals mark and salary equals five
thousand and let's create two other
customer objects so let's make a copy of
this customer object and let's change
the object name to customer date to and
here customer three and let's set ID to
maybe 110 Pam and maybe something like
six thousand five hundred and similarly
let's set this to maybe one nineteen is
the customer ID John is the name of the
customer and maybe his salary is three
thousand five hundred
okay now let's go ahead and create a
customer dictionary first of all this
dictionary class is present in system
that collection store generic namespace
so let's go ahead and bring that in
alright now when we create a dictionary
we need to specify the data type for its
key and value so basically remember a
dictionary is a collection of key value
pairs
okay so let's create a dictionary and
look at this the moment I open this
angular bracket in
it asks for the type for the key and the
type for the value so we are going to
create a customer's dictionary and the
key for this dictionary is going to be
the ID of the customer and the value is
going to be the customer object itself
okay so the key is going to be integer
because we want our key to be customer
ID and customer read IDs of type integer
and the value is going to be the
customer object itself so that pipe is
going to be customer and let's give this
dictionary a meaningful name let's call
this dictionary
maybe customers so we have just created
a customer's dictionary the type for the
key is integer and the value and I mean
the type for the value is customer ok
now let's add these customer objects
tour dictionary all right and to add
items to the dictionary we use add
method ok and look at this the moment I
open the bracket it prompts me the key
has to be integer and the value has to
be customer object so where do I get
customer one's ID from using the
customer one object so customer 1 dot ID
is going to give us the idea of customer
1 which is an integer type and we want
to store the object itself customer one
object and similarly let's go ahead and
store customer two and customer three
all right so at this point we have
created a dictionary and we added
customer objects to the dictionary okay
now we want to find customers within
this dictionary and the best way to find
a value within the dictionary is by
using its key what's the key here the ID
of the customer now let's say I want to
find the details of this customer who
has caught this ID 1 1 9 so the fastest
way to retrieve this customer object
from this dictionary is to use the key
for that dictionary the key here is
customer ID which is 1 1 9 so look at
this the moment I say dictionary of
customers open a square bracket look at
that it prompts me to enter the key ok
what is the key its customer ID of type
integer so we want the details of
customer 1 1 9 so I simply pass their ID
and look at what it is returning back
it's returning a customer object back so
let's do that in a variable of type
customer and maybe let's call this
customer 1 1 9 ok so we have just
retrieved a value from the dictionary
using its key alright now if I want to
print the details of this customer we
can simply use console dot readline
let's say I want to print the ID and I
also want to print name and then salary
as well
okay so where are we going to get the ID
from from this customer object so
customer one 19.8 a bear named and
finally their salary all right so let's
run this and see if we get the details
of customer whose ID is one one nine
there we go
the details match all right okay
so is it possible to loop through each
item within the dictionary absolutely
now if we have a list of customers for
example then we can loop through each
item within that list of customers using
a for each loop similarly here I have a
dictionary of customers so is it
possible to loop through each item
within that dictionary absolutely okay
so let's use a for each loop let's get
rid of this line right here so for eat
now if you have a list of customers then
you know that list is a collection of
customer objects but here this
dictionary is not as simple as saying
this dictionary is a collection of
customers it's actually a collection of
customers and their IDs so here we have
the key and a value okay so a dictionary
is a collection of key value pairs so
here when we loop through we have to use
key value pair because a dictionary
session Chile a collection of key value
pair of objects and when we use key
value pair we need to specify the type
of the key and the type of the value the
type of the key is customer ID which is
integer and the type of the value is
customer object itself and give this a
meaningful name and maybe let's call it
customer key value pair n dictionary
customers
okay now to get the key up from the key
value pair all you need to do is
customer key value pair dot key and look
at that what is it returning it is it is
returning an integer back nothing but
the ID of the customer so let's say we
want to print the ID console dot write
line ID equals so that should print the
ID now what is the value within this key
value pair it's nothing but the customer
object itself so look at this the moment
we say customer key value pair dot value
and look at the intelligence what is it
returning back it's returning a customer
object back so let's store that in a
variable of type customer maybe let's
call it cost all right now if we want to
get the old values out of this customer
object we can very easily do that using
the respective properties ID name and
salary so maybe let's go ahead and print
the ID name and salary so again to do
that ID equals maybe a placeholder there
similarly name equals and salary equals
all right so cost dot ID and similarly
customer dot name and customer dot
salary so when we run this as you might
expect it should loop through each
customer and then pull out there
probably let's call this key because we
are actually pulling out the key so we
know that's the key and this one is the
value and then maybe let's include a
dotted line here so that each customer
will be separated
all right so let's go ahead and run this
now it should loop through each customer
and print the values look at that we
have customer whose key is 1 0 1 1 10 1
19 and their respective details so you
can find you know values with an a'
dictionary either by using the key like
this which is the fastest way basically
to retrieve an item from the dictionary
or you can loop through each item within
the dictionary ok and keep in mind a
dictionary is a collection of key value
pairs
ok now here we are using a key value
pair now instead of using key value pair
we can also use an implicitly type 2
variable something like this wire ok now
if I run this it's still going to work
the same way let's go ahead and close
these windows here let me run this once
again look at that I have the same
output instead I mean the only change
here is we have changed you know the
datatype to where the implicitly typed
variable now it should be used this one
or should we use key value pair my
personal preference to use key value
pair because that way your code is more
readable rather than using this
implicitly typed variable because just
by looking at this code right now here I
can't tell what is the type of the key
and what is the type of value on the
other hand if you use key value pair
then you know you know what is the type
of the key and what is the type of the
value okay so your code is more readable
so as far as possible try avoid using
this ver keyword which is an implicitly
typed variable all right now is it
possible just to loop through the keys
within the dictionary absolutely if you
want to just get keys let's actually
comment this line so I want to loop
through you know through all the keys
within the dictionary if you want to do
that so dictionary object has got keys
property so which is going to return the
list of keys back now what are our key I
mean what is the data type of our key
it's nothing but an integer so we are
going to get an integer back
okay so let's call this maybe key and
then let's say console dot write line D
key so it should print out all the keys
now so let me go ahead and run this and
look at that we have all the keys
similarly is it possible to retrieve
only the values that are there within
the dictionary absolutely so instead of
using dot keys property all you need to
do is use dot values property but what
is value type it's nothing but a
customer which means we are going to get
a customer bag so let's call this maybe
customer and let's say cost is the name
of the reference variable let's get rid
of this one
let's uncomment this line so if you look
at this piece of code it's
straightforward all we are doing is we
are retrieving the ID name and salary
from that customer object so let's go
ahead and run this now and look at that
you get their values as expected all
right now another thing to keep in mind
is the keys within the dictionary must
be unique so if you look at this
dictionary this customers dictionary we
already have used these three keys one
zero one one ten and one nineteen so
what happens if I try to add let's get
rid of this code so what's going to
happen if I try to add maybe customer
one object once again when I build this
do I get a compile error no build
succeeded but then I plan this we kept a
runtime exception look at that
argument exception an item with the same
key has already been added so we already
have a key with the same I mean the same
key within the dictionary so we have
that exception so keys within the
dictionary must be unique when you try
to add them make sure you know the keys
the key doesn't already exist so how to
check if a key exists or not
again this dictionary object has a class
method called contains key okay so you
can specify the key that you want to add
there you can pass it as a parameter so
if that dictionary doesn't contain that
key then go ahead and add this so if
you're not sure whether the key is
present within a dictionary or not you
can use this contains key method it
returns a boolean a true or false so let
me run this now look at that we don't
get any error right now because this
piece of code wouldn't be executed
because the key is already there so this
line will be skipped not only while
adding even when you retrieve the values
from the dictionary using keys
make sure the dictionary
it has got the key before you try to
retrieve a value look at this when I say
customer maybe cost equals dictionary
customers and then let's say I want to
retrieve a customer object whose ID is
maybe 135 now that's this dictionary
contain a value with that ID no it
doesn't so what happens when I try to
build the solution look at this bill
succeeded we don't get any compiler
error but when I actually run this we
get an exception at runtime key not
found it exception so basically you try
to look up a key that doesn't exist so
you use this key that doesn't exist and
that's why we have that exception so
again check if the key exists or not how
do you do that the same idea so
dictionary customers dot contains key
whatever key that you are trying to look
up so if that key is present only then
execute this piece of code there are
several other useful functions within
this dictionary class we'll discuss them
in our next video session that's it for
today thank you for listening have a
great day
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Apr 29, 2026 Last updated
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