Part 81 When to use a dictionary over list in c# Video Lecture | C sharp: Enhance your Skills (English) - Back-End Programming

since part 81 of c-sharp tutorial in
this video we'll discuss a simple
example that demonstrates when to use a
dictionary over a list and c-sharp let's
create a simple console application when
we run it it should prompt us to enter a
country code and then if we enter a
valid at country code then the program
should display the name of the country
and its capital and then the program
should be in a loop so it should ask me
whether if I want to continue yes or no
if I enter any car page instead of sno
then it should keep asking the same
question do you want to continue as or
no so if I enter s then it should ask me
to enter the country code again if I
enter a valid country code then it
should display the name of the country
and its capital if I don't enter a valid
country code then it should print a
message stating country code not valid
and then again it should ask me whether
if I want to continue as I know if I say
no then the program should terminate
let's create the simple console
application so here I already have this
country class look at this it's very
straightforward with three auto
implemented properties named code and
capital and then within the main method
I've created five instances of this
country class so we have five countries
here Australia India US UK Canada all
right now first of all let's design this
program using a list collection class
okay so let's create a list so list of
country and let's call this list
countries equals new list of country and
then to this list let's add country
objects so list country start add
country one and similarly let's add
country two three four and five so
country two three four five so at this
point within this list we have five
countries so the first thing is we want
to ask the user to enter the country
code so console dot write line please
enter country code
and then obviously the user is going to
enter the country code let's store it in
a variable of type string and let's call
it STR country code equals and to read
whatever the user has entered on the
console we use console dot read line and
then let's convert that to uppercase
because look at this all the country
codes are in uppercase so let's convert
them to uppercase all right now what we
need to do we need to find that the
country object within this list you know
using that country code that the user
has entered and to find an object within
a list we can use find method and
obviously this is going to expect a
predicate where we can specify our
condition so find within that list of
countries a country such that country
dot cord equals whatever the user has
entered where I mean where do we have
the code that the user has entered in
this variable so let's compare it with
that and then obviously if a match is
found what does this method going to do
it's going to return that country object
back so let's store that in a variable
of type country and maybe let's call it
result country okay so if result country
equal to now then what does that mean
that means the country code for the
country code that the user has entered
we didn't find a match so in that case
we want to print a message stating
country code is not valid so country
code not valid if it is not now then we
know we have a matching country object
in which case we want to print the name
of the country and the capital
so name equals a placeholder there and
capital equals another placeholder all
right so let's plant the name of the
country and the capital all right
okay so let's go ahead and run this now
and see if it works so if I enter a
country called gbr for example look at
that I'm entering it in lowercase but
since we have converted that to
uppercase it should find it without any
problem so named United Kingdom capital
London and then look at this the program
is terminating now it asked me press any
key to continue and then once I press
any key the program is going to
terminate but instead of that we want
this program to be in a loop so let's go
ahead and use it develop we want only
these statements to be repeated okay
so let's use a do-while loop there so do
all this while some condition okay now
after we print you know the name of the
country and the capital what should we
do we should ask the user whether if he
wants to continue so let's ask that
question so do you want to continue
and obviously the user is going to
answer as I know so let's store use a
choice in a variable of type string so
let's call it STR user choice and to
read the user choice from the console we
use console dot readline and again let's
convert that to upper and one more thing
that we want to do here is we want to
tell the user that he can only enter as
or know okay so now we want to check if
this value that the user has entered is
s so we want to check that so while STR
use a choice so look at that I don't get
intellisense that's because this
variable is declared inside this - block
if we want that to be available here
then we need to declare that outside of
this - block so let's do that so string
STR use a choice let's initialize that
to an empty string all right so while
STR I use a choice equals yes then keep
repeating this piece of code so we have
all this code in a while loop okay and
another thing that I want to do here is
include another do-while loop so if the
user didn't enter yes or no if he
entered any carbage instead of yes or no
then we need to keep asking the same
question so let's put these two lines in
another do-while loop so keep doing
these statements in case if the user has
entered you know something else apart
from yes or no so if STR use a choice
not equal to no and if it is not equal
to
yes that means he has entered some
garbage instead of them in which case
repeat these statements that's what this
means so let's go ahead and run this and
see if it works as expected
ok look at that it's asking us to enter
the country code I and I and D it prints
the name of the country and capital it's
asking me do you want to continue I type
garbage tests look at that it keeps
asking the same question if I type yes
then please enter the country code if I
enter gbr look at that it prints the
country name and the code I mean the
capital do you want to continue no press
any key to continue once I press any key
the program terminates all right so the
output that we expect we are getting
that but then did we write that this
program in the best way possible
not really now if you look at the way we
are using this collection class here I
mean this list countries collection
primarily here we are using it for the
purpose of finding an object and find an
object with the within the collection we
are using a specific string that's the
country code so probably we can better
design this program by using a
dictionary okay so if our purpose is
primarily to lookup values then
dictionary is much better for
performance that's basically because
what's going to happen with this fine
method it's going to loop through these
objects within the list and then check
ok it checks for the first object is
your code you know whatever I and D if
yes return the object no then go to the
next object is your code ind no go to
the second and next object so it's going
to loop through each object within the
collection until a match is found and
once a match is found it's going to
return that object so obviously if you
have too many items within the
collection then the time to find within
that list you know the object that we
are looking for he's also going to
increase because it's going to loop
through all the objects ok but then
whereas when it comes to dictionary they
are very efficient in finding objects
using keys okay so in this case
dictionary would be a much better choice
for performance so fine method of the
list class look through each object in
the list until a match is found so if
you want to look up a value using a key
dictionary is better for performance
over lists so use dictionary when you
know the collection will be primarily
used for lookups okay
so let's rewrite this program using a
dictionary so instead of list of
countries I'm going to create a
dictionary and obviously when we created
a dictionary we need to specify a key as
well so the key for this dictionary is
going to be string because the country
code is a string and the value is going
to be the country object itself and
let's call this dictionary countries and
then obviously we want to create a new
dictionary okay so to this dictionary
let's go ahead and add items so
dictionary in countries dot add
obviously we need to specify the key as
well so the key is going to come from
the code property so we want the country
code to be its key and the value is
going to be the country object itself
all right so let's make copies of this
so this is going to be 5 4 3 2 and
similarly we need to change here 2 3 4
and 5 ok so we have our dictionary right
now now how to look up a value using
dictionary simply use dictionary of
dictionary countries off specify your
key so where are we going to get the key
from STR country code this variable so
we're going to pass that and look at
what this dictionary will return
obviously this dictionary is going to
return a country object back ok now
we're gonna have a slight problem with
this code that's because if the entered
code is not found within the dictionary
so if I enter country code like test
then this line is going to throw an
exception
so before we try to look up a key we
need to check if that key exists within
the dictionary and the way we do that is
by using contains key function so I'm
going to invoke this contains key and
then pass the key so STR country code
so obviously this function what is it
returning it's returning a boolean it
true or false if the key is present it's
going to return true in which case you
know look up the keys value within the
dictionary if the key is not present
within the dictionary then this result
country will be now
so if result country is now will print
that message country not valid otherwise
we'll print the name of the country in
capital the rest of the program remains
unchanged here we are now using a
dictionary instead of a list so let's
run this of this build errors let's
check that so we need to include those
brackets so let's run this now okay
please enter country code let's enter
IND so name of the country and capital
do you want to continue yes so it asks
the country code to enter again let's
say gbr so we get the output as expected
do you want to continue I type you know
garbage again it keeps asking the same
question when I type no the program is
going to terminate okay all right now we
have seen you know creating a simple
console application let's create a
simple web form as well okay look at
that this is what we want to achieve on
a web form we need three text boxes the
first text box should enter the should
ask the user to enter the country code
if I enter an invalid country code then
we want a message like this country code
not found on the other hand if we enter
a valid country code then we want to
display the name of the country and its
capital let's see how to achieve this so
I already have created a web application
here in asp.net web application the
first step is to obviously add the
country class so let's add a class file
and maybe let's call that country dot CS
and then into this class let's copy the
country definition and paste it from our
controller
application all right the next thing is
to add a webform so let's go and add a
webform and let's call it web from one
dot aspx and then let's set you know the
style attribute all right now let's
quickly design this waveform so we need
a table with two TDs okay so we need
basically four rows and each row should
contain two TDs
so Apr let's include a TD and then
another TD here right so let's make
copies of this one two three and four
alright in the first row what do we want
we want you know this text country code
and text box so let's say country code
and then we need a text box so let's
drag and drop that from the tool box so
we need two other text boxes so let's
make a copy of this and then put into
these TD's all right and then one more
thing is we need a border for this table
so let's set the border so we need a
table tag in the first place we directly
have TR within the div tag so let's move
the closing table tag right here all
right so to this table let's go ahead
and set the style attribute and then
maybe let's set border to one pixel
solid black color alright and maybe
let's call this txt country code because
that's in the first text box will enter
country code and in the next row we want
to display the name of the country so
that will be the label and maybe let's
call this D Eckstein
and then in the final text box we are
going to display capital and let's call
this text box txt capital maybe right
and then in the last table row we want a
label control which is going to display
you know a message if the country code
is not found so what I'm gonna do is I'm
going to have just one TD here but then
the width of that TD should span across
to t DS so let's use call span equals
two and then let's drag and drop in
label control there alright and then we
don't want any text initially within the
label so let's get rid of this property
and then we want the for color to be red
so let's set that to red all right so we
have designed the waveform all right now
within the code-behind file first of all
whenever the text in the text box
changes we want to immediately post back
to the web server so let's go and set
auto post back property to true and then
obviously this text box raises text
change event so double pick that the
event handler will be generated so here
we are going to write the code so within
the page load what I'm going to do is
I'm going to copy the same code from our
console application so we're going to
create the country objects and we are
going to create that dictionary okay so
here we have the dictionary and then
what I'm going to do is I'm going to put
this dictionary in a session variable
maybe let's call it country's data
so in the name of the dictionary is
dictionary country so let's put it
within the session variable and the
reason why I'm doing that I'm putting it
in the session variable is we don't want
to be building this country's dictionary
every time we load the page okay we load
it once and then retrieve it from the
session so if the webform
I mean this dictionary can be used on
different web forms as well and when
this waveform is loaded multiple times
you know this piece of code will not be
executed because we are going to put a
condition here if execute this piece of
code
only if session of countries data equal
to now meaning in the session if we
don't have any countries data only then
try to create the list and then populate
the I mean try to create the dictionary
and then populate it with these items
and then we put that in session and
within the text change the event of the
drop-down list what we are going to do
we are going to simply retrieve that
dictionary out of the session variable
so let's copy that so we are going to
get a dictionary from the session
variable so let's create a variable of
type dictionary the key is going to be
string and the object is going to be I
mean the value is going to be country
object so let's call this dictionary
countries okay now whatever we get back
from the session it will be an object it
will be of type object so we need to
typecast that to be of type dictionary
so let's use the typecast operator and
typecast that okay at this point we have
our dictionary of customers so what I'm
gonna do here is copy this piece of code
so if dictionary countries dot contains
case so if this dictionary contains the
key so where are we going to get the key
from the user is going to enter the key
within this text box txt country code so
let's use that text box here txt country
code dot text is going to give us the
country code but then we need to convert
that to upper in case if the end user
enters it in lowercase they still need
to find it so the same code let's copy
it there so if the dictionary contains
that key then return the keys value from
the dictionary else store now within
this variable and if result country is
now what we want to do this is not a
control application this is a web
application so we want our text box txt
name dot text to be populated with
reserved the country dot name and
similarly we want txt capital textbox to
be populated with capital ok and then we
also want to we have a label here which
we are using to display you know the
message country code not found so let's
give it a meaningful ID so let's call it
LVL message and within our cord behind
file if the country code is found then
simply set the text of this label to an
empty string okay that's because if
previous time the error was displayed
and next time when you enter a valid can
record we want that to be cleared okay
that's why we are setting to empty text
here and then if it's not null obviously
we have found it oh so if it's now
obviously what does that mean we didn't
find it in which case we
to display an error message within the
label so country code not valid okay
let's copy that and paste it here let's
set it to an empty string okay so if it
is not now then within the text boxes
display the name and capital as simple
as that so let's go ahead and run this
now so let's enter a valid country code
so gbr and look at that the moment I
click away
I find name and capital if I enter an
invalid country code country code not
valid and one more thing that we want to
do is we want to clear these two text
boxes because for test country code
these are not the name in capital so
let's do that
so what we need to do here is txt
capital dot text equals empty string and
similarly txt name dot text equals an
empty string let's run this one more
time test
look at that country code not valid if
we enter a valid country code we see
that and if I again entered test gets
cleared tentacle not valid all right
that's it for today thank you for
listening
have a great day