Back-End Programming Exam > Back-End Programming Videos > C sharp: Enhance your Skills (English) > Part 75 List collection class in c# continued
Part 75 List collection class in c# continued Video Lecture - C sharp Enhance
Text Transcript from Video
this is part 75 of c-sharp tutorial in
this video we'll continue discussing
list collection class in c-sharp this is
continuation to path 74 so please watch
part 74 from the c-sharp tutorial before
proceeding with this video we'll be
discussing all these functions first
let's look at this contains function
this function checks if an item exists
in the list and if an item does exist in
the list then this method returns true
otherwise false let's look at that in
action we'll be using this customer
class in this demo
notice that this class is very simple
with three auto implemented properties
ID name and salary and within the main
method we are creating three instances
of this customer class customer one
customer to end customer three and then
we are creating a list of customers and
to that list we are adding customer one
customer to end customer three objects
now let's check if customer three object
exists in the list and to do that we can
use contains method so contains and look
at that this method expects an object of
type customer so let's go ahead and pass
customer three object and look at the
return type it's a boolean meaning it's
going to return a true or false if the
object exists it returns true otherwise
false and let's say if the object exists
we want to print a message stating
customer three objects exists in the
list else we want to print a message
stating customer three object does not
exist in the list so since customer
object the customer three object is
there we should get that message now
let's remove that object from the list
so we only have at the moment customer
one and customer two object in the list
let me run this now and look at that
customer three object does not exist in
the list all right now let's look at
using exists function now this function
also checks if an item exists in the
list but based on a given condition okay
and again if the item exists within the
list and this method is going to return
true
otherwise false so for both of these
methods the return type is a boolean
okay so let's see how to use exist
function first of all let's go ahead and
add customer 3 object as well all right
now when I use exists function look at
that it asks me to pass a predicate so
which means we can pass a lambda
expression here now let's say I want to
check whether if this list contains a
customer whose names name starts with P
okay now we do have a customer object
whose name starts with P so if I want to
base my search based on that condition
then I can use this exist function so we
need to pass a lambda expression here so
we have you know this list of customers
contain a customer object so let's say
customer such that customer dot name dot
starts with maybe letter P and we do
have a customer whose name starts with P
so it should say customer 3 I mean it
should come into this if block and print
this message so let me actually run this
look at that customer 3 objects exist in
the list on the other hand you know we
don't have a customer whose name starts
with said ok so obviously when we run
this the method should return false and
it should come to the else part and
print this message ok customer 3 object
does not exist in the list now you can
give any kind of message that you want
here just in the interest of time I
didn't change that message there all
right so the only difference between
contains and exists is that with exists
function you can specify a condition but
what contains you can't do that you pass
the object itself to that function now
let's look at using find function so
this function searches for an element
that matches the conditions defined by
the specified lambda expression and then
it returns the first matching item from
the list ok so again this condition
I mean this function expects a condition
to be passed and then even if there are
several items matching that condition
this function is going to only return
the first matching item from the list
let's look at using that ok now let's
say if you look at these employees you
know there are two employees whose
salary is greater than 5,000 customer
two and customer three now let's use
find method so let's get rid of this
piece of code so list customers dot find
and look at that again we need to pass a
predicate so let's pass a lambda
expression so let's say customer such
that customer dot salary greater than
5,000 okay now look at the return type
of this function unlike contains and
exists this function actually returns a
customer object so this fine function is
going to return the actual object back
okay whereas contains and exists return
a boolean it only tells you whether the
object exists in the collection or not
but then this fine function is going to
find that object if it exists it's going
to return that
okay so let's store the returned object
in a variable of type customer and maybe
let's call it C okay and look at this it
only returns one customer object back
the fine method and then maybe we want
to print out the details of that
customer maybe their ID name and salary
and to speed things up I have already
typed that so ID equals name equals
error equals we have placeholders there
and then we are basically printing their
ID name and salary so let me go ahead
and run this and see if it's going to
print the details of that employee look
at that it has printed the details of
Pam so Pam is the first matching
customer whose salary is greater than
5,000 so it doesn't give you the second
okay all right
now let's look at using find last
function again this function searches
for an element that matches the
conditions that are defined by the
specified lambda expression and then
this method is going to return the last
matching item from the list okay so if
there are multiple items that matches
the given condition then this fine last
function returns the last matching item
okay so the same function I mean the
same cord but then instead of using find
you know I'm going to use find at last
and again this method expects a
predicate so we are passing this lambda
expression here at this point it should
actually written as this customer that
is robbed so let's run this and see if
it works that way and look at that we
get robbed whose salary is greater than
5,000 so that's the difference between
fine and fine last find is going to
return the first matching item
whereas fine last is going to return the
last matching item both based on a given
condition all right if you want all the
items then we have find all function so
let's look at using find all function so
obviously if you look at this function
find all look at the return type instead
of returning a single customer bag it is
returning list of customers back ok so
which means this is going to return all
the customers who match the given
condition from the list
okay so let's include list here so list
of customer and maybe let's call it
customers and then since we have a list
here let's loop through and print the
details and let's use a for each loop so
for each customer and let's call it C in
our customers collection
so we are basically printing out their
ID name and salary again so let's run
this and see if we get both the
employees look at that I get both the
employees who I mean both the customers
whose salary is greater than 5,000 okay
all right now let's look at using this
find index function so obviously find
index returns the index of the first
item that matches the condition
specified by the lambda expression and
there are two overloads of this method
which allows us to specify that range of
elements to search within that list
let's look at that in action so we have
this list of customers here now let's
say I want to find index so find index
returning an integer so it's going to
return the index of the matching element
so we need to specify again a lambda
expression here let's use the same
lambda expression customer dot salary
greater than 5,000 and let's say end may
be index equals that and then let's
print the index
okay so we have two employees whose
salary is greater than 5,000 so this
should now return the index of customer
to object and the index of customer to
object is one because the index is zero
paced so customer one is zero and
customer two is one and thus find index
method is going to return only the first
matching items index now there are two
customer objects which match this
condition but they are only going to get
the index of the first matching customer
so let's run this and look at that index
is one as expected now find last index
is going to return the last matching
items index we'll come back to that in
just a bit but then look at this this
find the index method has got several
overloads as well so we have through
three overloads here so basically here
we are only specifying the condition but
the next overload you can also specify
the start index so at what point in the
list do you want to start searching do
you want to start searching at position
zero opposition one opposition - you can
specify that as well you saying you know
this overload where we can specify the
index so let's specify the index as two
so if we specify zero one two as the
index then we are going to get this
customer object so let's specify the
index s - and now it should give us zero
one two as the index let's run this and
look at that
so it's giving us you know from here the
matching element is customer three and
customer three index within the list is
three and we get that I mean sorry -
okay and there is another overload as
well so if you have several items in the
list not only can you specify the start
index you can also specify from that
start index how many items you want to
look up okay
so it's going to you know look in the
range of those elements and then return
the index of the first
my element okay now similarly we have
another method find last index so this
is going to return the index of the last
matching element okay
so let's call let's invoke fine last
index and again this method also has got
three overloads
and the use cases are the same okay so
now this should return the index of
customer 3 object which is 2 because
there are two matching elements but this
function is going to return the index of
the last matching element so let's go
ahead and run this so index is 2 all
right now let's look at converting an
array to a list so how do we convert an
array to a list simply use this to list
method so first of all let's get rid of
this code here and then let's create an
array so customer and maybe let's call
it customer array equals new customer
array and then let's create let's say
the array size to 3 customer array of 0
equals customer 1 and similarly let's
initialize the array with the rest of
the customer objects
all right now I want to convert this
array to a list all we need to do is
customer array dot to list and look at
the return type of this function it is
returning a list back ok so basically we
can store that in a list types or list
customer and let's call it maybe list
customers and then obviously you can use
a for each loop and loop through each
customer object and print their details
so for each customer see in list
customers so this will verify that the
list is I mean the array is successfully
converted to a list and just to speed
things up we have that already type so
let's copy and paste it there let's run
it now and we should get all the three
customers ok
similarly we can convert a list to an
array ok so here at the moment let's get
rid of this one and let's say list
customers equals new list of customer
and then to this list let's add customer
objects the list customers dot add
customer one object and let's add
customer two and customer three as well
now to convert this list into an array
if you simply say list customers to
array and look at the return type what
do we get back customer array so you can
store those elements in an array of type
you know customers and then loop through
them in the same manner okay and we can
also convert a list to a dictionary and
to do that again you use two dictionary
very simple and straightforward let's
look at that actually so let's convert
this list to a dictionary so when we say
list dot two dictionary and obviously
when you want to convert a list to a
dictionary you need to specify the key
for the dictionary and then the value
for the dictionary okay now value part
is optional since this list of customers
by default if you don't specify the
value
then the value is going to be that
customer object so let's just specify
the key so I want the key to be the ID
of the customer so obviously this is
going to return a dictionary back so
dictionary of key you know the type is
going to be the key of the dictionary is
going to be integer and the value is
going to be customer and let's call it
maybe dictionary equals you know
whatever this function is returning
now let's loop through that dictionary
and dictionary is a collection of key
value pair so for each key value pair
key is going to be of type integer value
is going to be of type customer and
let's call this maybe kbp key value pair
in the given dictionary so we are going
to loop to that dictionary and then
obviously if you want to get the key
from the key value pair you simply say
key okay and then let's say we want to
print that so control dot readline key
equals K V P dot key and then we want to
print the details of the customer I mean
the value as for all the value is
nothing but the customer object so let's
get the customer object let's set the
variable name as C and how do I get the
value simply say key value pair dot
value and look at that it's going to
written a customer object back and then
here we are printing ID name and salary
of that customer so let's go ahead and
run this now and we should see the
respective keys and value objects all
right that's it for today thank you for
listening have a great day
this video we'll continue discussing
list collection class in c-sharp this is
continuation to path 74 so please watch
part 74 from the c-sharp tutorial before
proceeding with this video we'll be
discussing all these functions first
let's look at this contains function
this function checks if an item exists
in the list and if an item does exist in
the list then this method returns true
otherwise false let's look at that in
action we'll be using this customer
class in this demo
notice that this class is very simple
with three auto implemented properties
ID name and salary and within the main
method we are creating three instances
of this customer class customer one
customer to end customer three and then
we are creating a list of customers and
to that list we are adding customer one
customer to end customer three objects
now let's check if customer three object
exists in the list and to do that we can
use contains method so contains and look
at that this method expects an object of
type customer so let's go ahead and pass
customer three object and look at the
return type it's a boolean meaning it's
going to return a true or false if the
object exists it returns true otherwise
false and let's say if the object exists
we want to print a message stating
customer three objects exists in the
list else we want to print a message
stating customer three object does not
exist in the list so since customer
object the customer three object is
there we should get that message now
let's remove that object from the list
so we only have at the moment customer
one and customer two object in the list
let me run this now and look at that
customer three object does not exist in
the list all right now let's look at
using exists function now this function
also checks if an item exists in the
list but based on a given condition okay
and again if the item exists within the
list and this method is going to return
true
otherwise false so for both of these
methods the return type is a boolean
okay so let's see how to use exist
function first of all let's go ahead and
add customer 3 object as well all right
now when I use exists function look at
that it asks me to pass a predicate so
which means we can pass a lambda
expression here now let's say I want to
check whether if this list contains a
customer whose names name starts with P
okay now we do have a customer object
whose name starts with P so if I want to
base my search based on that condition
then I can use this exist function so we
need to pass a lambda expression here so
we have you know this list of customers
contain a customer object so let's say
customer such that customer dot name dot
starts with maybe letter P and we do
have a customer whose name starts with P
so it should say customer 3 I mean it
should come into this if block and print
this message so let me actually run this
look at that customer 3 objects exist in
the list on the other hand you know we
don't have a customer whose name starts
with said ok so obviously when we run
this the method should return false and
it should come to the else part and
print this message ok customer 3 object
does not exist in the list now you can
give any kind of message that you want
here just in the interest of time I
didn't change that message there all
right so the only difference between
contains and exists is that with exists
function you can specify a condition but
what contains you can't do that you pass
the object itself to that function now
let's look at using find function so
this function searches for an element
that matches the conditions defined by
the specified lambda expression and then
it returns the first matching item from
the list ok so again this condition
I mean this function expects a condition
to be passed and then even if there are
several items matching that condition
this function is going to only return
the first matching item from the list
let's look at using that ok now let's
say if you look at these employees you
know there are two employees whose
salary is greater than 5,000 customer
two and customer three now let's use
find method so let's get rid of this
piece of code so list customers dot find
and look at that again we need to pass a
predicate so let's pass a lambda
expression so let's say customer such
that customer dot salary greater than
5,000 okay now look at the return type
of this function unlike contains and
exists this function actually returns a
customer object so this fine function is
going to return the actual object back
okay whereas contains and exists return
a boolean it only tells you whether the
object exists in the collection or not
but then this fine function is going to
find that object if it exists it's going
to return that
okay so let's store the returned object
in a variable of type customer and maybe
let's call it C okay and look at this it
only returns one customer object back
the fine method and then maybe we want
to print out the details of that
customer maybe their ID name and salary
and to speed things up I have already
typed that so ID equals name equals
error equals we have placeholders there
and then we are basically printing their
ID name and salary so let me go ahead
and run this and see if it's going to
print the details of that employee look
at that it has printed the details of
Pam so Pam is the first matching
customer whose salary is greater than
5,000 so it doesn't give you the second
okay all right
now let's look at using find last
function again this function searches
for an element that matches the
conditions that are defined by the
specified lambda expression and then
this method is going to return the last
matching item from the list okay so if
there are multiple items that matches
the given condition then this fine last
function returns the last matching item
okay so the same function I mean the
same cord but then instead of using find
you know I'm going to use find at last
and again this method expects a
predicate so we are passing this lambda
expression here at this point it should
actually written as this customer that
is robbed so let's run this and see if
it works that way and look at that we
get robbed whose salary is greater than
5,000 so that's the difference between
fine and fine last find is going to
return the first matching item
whereas fine last is going to return the
last matching item both based on a given
condition all right if you want all the
items then we have find all function so
let's look at using find all function so
obviously if you look at this function
find all look at the return type instead
of returning a single customer bag it is
returning list of customers back ok so
which means this is going to return all
the customers who match the given
condition from the list
okay so let's include list here so list
of customer and maybe let's call it
customers and then since we have a list
here let's loop through and print the
details and let's use a for each loop so
for each customer and let's call it C in
our customers collection
so we are basically printing out their
ID name and salary again so let's run
this and see if we get both the
employees look at that I get both the
employees who I mean both the customers
whose salary is greater than 5,000 okay
all right now let's look at using this
find index function so obviously find
index returns the index of the first
item that matches the condition
specified by the lambda expression and
there are two overloads of this method
which allows us to specify that range of
elements to search within that list
let's look at that in action so we have
this list of customers here now let's
say I want to find index so find index
returning an integer so it's going to
return the index of the matching element
so we need to specify again a lambda
expression here let's use the same
lambda expression customer dot salary
greater than 5,000 and let's say end may
be index equals that and then let's
print the index
okay so we have two employees whose
salary is greater than 5,000 so this
should now return the index of customer
to object and the index of customer to
object is one because the index is zero
paced so customer one is zero and
customer two is one and thus find index
method is going to return only the first
matching items index now there are two
customer objects which match this
condition but they are only going to get
the index of the first matching customer
so let's run this and look at that index
is one as expected now find last index
is going to return the last matching
items index we'll come back to that in
just a bit but then look at this this
find the index method has got several
overloads as well so we have through
three overloads here so basically here
we are only specifying the condition but
the next overload you can also specify
the start index so at what point in the
list do you want to start searching do
you want to start searching at position
zero opposition one opposition - you can
specify that as well you saying you know
this overload where we can specify the
index so let's specify the index as two
so if we specify zero one two as the
index then we are going to get this
customer object so let's specify the
index s - and now it should give us zero
one two as the index let's run this and
look at that
so it's giving us you know from here the
matching element is customer three and
customer three index within the list is
three and we get that I mean sorry -
okay and there is another overload as
well so if you have several items in the
list not only can you specify the start
index you can also specify from that
start index how many items you want to
look up okay
so it's going to you know look in the
range of those elements and then return
the index of the first
my element okay now similarly we have
another method find last index so this
is going to return the index of the last
matching element okay
so let's call let's invoke fine last
index and again this method also has got
three overloads
and the use cases are the same okay so
now this should return the index of
customer 3 object which is 2 because
there are two matching elements but this
function is going to return the index of
the last matching element so let's go
ahead and run this so index is 2 all
right now let's look at converting an
array to a list so how do we convert an
array to a list simply use this to list
method so first of all let's get rid of
this code here and then let's create an
array so customer and maybe let's call
it customer array equals new customer
array and then let's create let's say
the array size to 3 customer array of 0
equals customer 1 and similarly let's
initialize the array with the rest of
the customer objects
all right now I want to convert this
array to a list all we need to do is
customer array dot to list and look at
the return type of this function it is
returning a list back ok so basically we
can store that in a list types or list
customer and let's call it maybe list
customers and then obviously you can use
a for each loop and loop through each
customer object and print their details
so for each customer see in list
customers so this will verify that the
list is I mean the array is successfully
converted to a list and just to speed
things up we have that already type so
let's copy and paste it there let's run
it now and we should get all the three
customers ok
similarly we can convert a list to an
array ok so here at the moment let's get
rid of this one and let's say list
customers equals new list of customer
and then to this list let's add customer
objects the list customers dot add
customer one object and let's add
customer two and customer three as well
now to convert this list into an array
if you simply say list customers to
array and look at the return type what
do we get back customer array so you can
store those elements in an array of type
you know customers and then loop through
them in the same manner okay and we can
also convert a list to a dictionary and
to do that again you use two dictionary
very simple and straightforward let's
look at that actually so let's convert
this list to a dictionary so when we say
list dot two dictionary and obviously
when you want to convert a list to a
dictionary you need to specify the key
for the dictionary and then the value
for the dictionary okay now value part
is optional since this list of customers
by default if you don't specify the
value
then the value is going to be that
customer object so let's just specify
the key so I want the key to be the ID
of the customer so obviously this is
going to return a dictionary back so
dictionary of key you know the type is
going to be the key of the dictionary is
going to be integer and the value is
going to be customer and let's call it
maybe dictionary equals you know
whatever this function is returning
now let's loop through that dictionary
and dictionary is a collection of key
value pair so for each key value pair
key is going to be of type integer value
is going to be of type customer and
let's call this maybe kbp key value pair
in the given dictionary so we are going
to loop to that dictionary and then
obviously if you want to get the key
from the key value pair you simply say
key okay and then let's say we want to
print that so control dot readline key
equals K V P dot key and then we want to
print the details of the customer I mean
the value as for all the value is
nothing but the customer object so let's
get the customer object let's set the
variable name as C and how do I get the
value simply say key value pair dot
value and look at that it's going to
written a customer object back and then
here we are printing ID name and salary
of that customer so let's go ahead and
run this now and we should see the
respective keys and value objects all
right 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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