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‫And the last videos we talked about hash tables.

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‫So in this lesson, we discuss how the generic version of hash tables looks like and the generic version

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‫of hash table is dictionary.

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‫So we're going to see how to use dictionaries in this video.

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‫So similar to a hash table, a dictionary will store its value and a key value pair like we had with

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‫the dictionary, right where we said the key value pair for auto would be car.

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‫So the key would be auto, which is the German word for car.

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‫And then car is going to be the value that is inside of this dictionary.

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‫So that's a real world dictionary in a German English dictionary, for example.

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‫But now we're going to use programming dictionaries.

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‫So C-sharp dictionaries, which have a key value pair like we have here, where we store the value assigned

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‫at a specific key.

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‫So.

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‫Let's go ahead and define a dictionary.

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‫So from the Microsoft documentation, the dictionary is defined like so.

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‫So it's going to look something like this dictionary rt value.

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‫So what that basically means is that we need to specify the types of both our keys and values in the

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‫declaration similar to how we did it, for example, for a list.

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‫So a list also needed to have a specific type.

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‫A list could be of type integer, it could be of type string, it could be of type object and so forth.

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‫But we needed to define of what type this list has to be.

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‫The same goes for dictionary, but there we have to define it for the key as well as for the value.

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‫So that's basically what this key and RT value means.

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‫So that means that we have a lot of flexibility, but not the flexibility that we had in a hash table.

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‫So we basically can go ahead and create a dictionary like this one here where we say that the key will

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‫be of type integer and the value will be of type string.

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‫And of course, in order to use dictionaries, we need to make sure that we have using system that collections

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‫are generic.

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‫So you see a dictionary is a generic collection.

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‫We saw in another video that there is a difference between generic and non generic collections.

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‫So hash tables or non generic collections and dictionaries are generic collections, so they have all

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‫of the advantages and disadvantages.

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‫So now this dictionary will have an integer, a number, so to speak, and a value that will be a string.

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‫So the number will be the key and the string will be the value.

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‫Now here we're creating this dictionary called my dictionary, and we're initializing it with an empty

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‫dictionary straight away.

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‫At this point, we can then go ahead and use this dictionary so we can add values to that dictionary.

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‫We can, for example, also already define the values of that dictionary straight away.

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‫So in the same line, basically right here.

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‫So we could, for example, just say, okay, this is going to be how the dictionary is going to look

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‫like.

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‫Where we have an integer and a string.

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‫So we have the one being this integer here, the key and the one being the text for it would be the

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‫value.

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‫So now we have the integer type and then the spoken English word for whatever this integer is.

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‫So one would be one, two would be two, three would be three and so forth.

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‫Now, of course, dictionaries are not limited to integers and strings.

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‫We can use much more complex values that we are storing.

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‫So for example, let's consider this class here.

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‫So I'm creating a new class called employee.

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‫I'm going to put it in the same file, but of course you could create a separate file.

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‫So we have a few properties like row, name, age and rate for every single employee.

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‫And then we have the salary, which is a float, and it returns the rate of eight times, five times

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‫four times 12.

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‫So whatever the rate is, times, this value is going to be what we're going to store or get as the

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‫salary.

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‫So if we were to retrieve the salary, it will directly calculate the salary for us.

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‫So that's 8 hours times five days times four weeks times 12 months.

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‫So that's how it's going to calculate basically the yearly salary, so to speak.

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‫Of course, times the rate.

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‫So now let's say we have a database of employees.

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‫Let's.

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‫I assume that this is going to be our database of employees.

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‫And by the way, I just realized that I missed the rate here when creating the constructor.

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‫So this constructor is just going to also use the rate now and assign the rate here and now we can use

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‫our data from the database.

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‫So we have the database where we get the title, we get the name, we get the what is it, the age super

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‫old lady, 95 years old.

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‫And then we have her rate.

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‫So she has a rate of 200.

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‫Then we have the manager, Joe, who is 35, has a rate of 25 and so forth.

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‫So now what I'm going to do is I'm not going to use this dictionary here.

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‫I'm going to create a separate dictionary that I'm going to call employees directory.

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‫And that employee directory will basically have a key value pair of string employee.

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‫So it will store for a specific string the entire employee object.

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‫And I'm going to call this employees directory and the string that we're going to use is going to be

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‫the employees role.

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‫Okay.

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‫So here I'm going to use this for each loop that will now go through every single employee in my employees

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‫database.

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‫So this is my employees database.

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‫I'm faking it, so to speak.

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‫Right?

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‫It's going to go through every single item of that employee state database and it's going to add to

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‫my employees directory at the position or at the key of the role, the employee itself.

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‫So here we're assuming that for every single role we only have one employee, otherwise this would screw

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‫the whole system up.

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‫So this is an example of how we can create a dictionary with data from a fake database, which is basically

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‫just going to be an array of employees that we have defined here.

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‫So now what if we want to get the data from a dictionary?

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‫So we want to fetch data from a dictionary and let's say we want to fetch data of the employee that

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‫is the CEO.

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‫So that has the position of the CEO.

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‫Then we can go employee I'm going to call this one Apple and we get it from the employees directory

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‫and here we just say, okay, I want to have the CEO, so I want to know the person and maybe also the

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‫entire object actually of the person that has CEO as their title.

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‫Basically just saying the where the key is going to be CEO for my dictionary employee, stick to a directory

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‫there.

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‫I want to know who is the CEO and want to store the entire employee in an object.

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‫So now I can go ahead and display the details of that employee using a console right line statement

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‫like so.

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‫So here I say the employee name will, which will be ample name, then the role as well as the salary.

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‫So this will be displayed.

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‫Okay.

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‫So basically we'll get the salary based on the rate and this calculation here.

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‫It will get the role directly and will get the name directly from the employee object itself.

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‫So from this Apple object.

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‫So now let's run this real quick and see what queen is going to earn, considering that she works full

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‫time and we can see she has a salary of 384,000.

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‫Her name is Gwen, her role as CEO.

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‫So running this code works.

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‫As you see, there's no problem here.

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‫But the problem could be that we are entering a wrong value.

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‫So let's say instead of CEO, I'm searching for the CTO, so for the technical officer, so the Chief

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‫Technical Officer and if I run this, you see my application crashes.

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‫So it says CTO was not present in the dictionary, so the key was never given.

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‫So in order to fix that, we can basically check if the key exists.

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‫So here what would be a very good way of checking.

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‫This would be to create a key called SEO or string called key, which has the value of SEO.

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‫And then we check the employees directory.

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‫For that particular key.

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‫So here you see contains key is one of the favorite or favorite options here.

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‫So contains key.

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‫And then here we can pass the string that we want to check as the key.

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‫So does it contain the key called CEO?

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‫If it does, then run this code here.

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‫And if it doesn't, then don't run it.

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‫Or you could, of course, also just say this key doesn't exist.

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‫So now you could create a little application that is going to allow you to enter a key and then your

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‫application will check.

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‫Okay, does this exist or not?

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‫And by the way, here this should be replaced with key.

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‫It's not going to be hardcoded anymore.

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‫Well, it's hardcoded in at another point, so to speak.

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‫But this could be something that we get from user input or the user can select it from a UI or something

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‫like that, and then the application would retrieve the data and display this instead of just in a console

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‫application in an actual UI.

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‫And you will later see how to use UI's or how to build your eyes using WPF.

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‫So that is one way of getting around the problem.

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‫Another way would be to use something called try get value.

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‫So let me quickly add a little bit of code and go over it.

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‫So let's say we have this empty employee, which I call result, and it's empty because I set it to

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‫null and then I'm checking the employees directory.

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‫If it has the value called intern and I'm using this try get value method.

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‫So this try and get value method will return a boolean, which is great because that's what an IFF statement

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‫likes to have in the condition and it will print out the result and it will put the value into result.

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‫So this result will actually be an employee.

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‫So try get value.

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‫We'll try to get the value that we pass here.

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‫And if it worked, the volume will return true.

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‫So this statement will be executed and at the same time it will get what put the result into this variable

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‫so the out will be put into this result variable.

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‫So the value that we retrieve from our employees directory will be stored in result.

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‫So that's what this statement here says.

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‫And if it worked, in fact, and intern does exist, then this code will be executed and otherwise this

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‫code will be executed.

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‫So this key does not exist.

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‫So that would be just another way of getting around the same issue.

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‫So try get value also works well.

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00:12:11,640 --> 00:12:21,060
‫So value retrieved employee name Ernest Intern 22 and he gets a salary of €15,000 a year or whatever

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‫type of money you want to talk about here.

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‫Okay.

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‫So now let's dig a little bit deeper because we can also get an element with the element at method,

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‫so an element of our dictionary.

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00:12:37,290 --> 00:12:43,650
‫So as we learned or as you learned, a dictionary is going to use structs here.

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00:12:43,740 --> 00:12:50,280
‫So a dictionary is a collection of key value pairs, which is a struct that is defined like a key value

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‫pair that is going to look something like this here.

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‫So let's look at it this year.

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‫So we have the key and the value.

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‫So this is the key value pair.

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‫So that's what a dictionary is containing.

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00:13:05,100 --> 00:13:12,030
‫So let's look at this for a loop here and let me I can actually put it right here.

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‫So this for loop, what it will do is it will use this element add method.

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‫However, in order to use it, we will need to implement the link.

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‫So for now, just accept that link is a powerful tool that allows us to work with collections in a very

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‫efficient way and we will have an extra chapter later on where we will look into link specifically,

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‫but for now let's just accept it as that.

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‫So once you get to the later chapters, you will learn more about it and then this will make more sense.

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‫So in our case.

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‫And this particular example where we have our key value pair with the key and value where key.

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‫Is the type of our keys of our dictionary.

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‫And the same goes for the RT value, which is the value of our dictionary.

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‫Now in our case, it's string and employee if we look at it.

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‫So for our dictionary that we created here, it's string and employee.

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‫But internally behind this string key, there is also an integer value, so a number, so to speak.

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‫So let's say at position zero will be the CEO at position one, the manager at position two, the air

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‫person at position three, the secretary and so forth.

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00:14:39,380 --> 00:14:46,490
‫Even though they will all be at the position so at the key of their role, but internally they will

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‫also be at a number.

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‫So the key will also be a number internally.

191
00:14:52,190 --> 00:14:56,450
‫So that's exactly what we can use for this element at.

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00:14:56,870 --> 00:15:04,400
‫So this element and if you hover over it returns the element at the specified index in a sequence.

193
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‫So a dictionary is a sequence.

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00:15:07,610 --> 00:15:15,100
‫So it will return basically our employee position zero, our employee at position one, our amplitude

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‫position two and so forth.

196
00:15:17,330 --> 00:15:24,590
‫However, this will return a key value pair and the key value pair we are going to create here is going

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‫to be of type, string and employee.

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00:15:26,900 --> 00:15:37,190
‫So now we can display the key and then we can get the value of our employee at our key value pair at

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‫the value position.

200
00:15:39,230 --> 00:15:47,660
‫Because we get it from our element at this is a little more complicated, but basically it is just another

201
00:15:47,660 --> 00:15:57,770
‫way to access an item inside of your dictionary, not using the key as a string, but the key as an

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‫integer.

203
00:15:58,160 --> 00:16:00,680
‫And this goes for all different kinds of keys.

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‫So no matter what type you used for the key, there is always a number assigned to it as well.

205
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‫So even if this was off type object or if this was of type double or whatever, there is always an integer

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‫assigned to it which is allowing us to use this element at at I.

207
00:16:19,310 --> 00:16:26,210
‫So let's go through this and you will see that this will basically allow us to display all employees.

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‫So it goes through all employees in our list.

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00:16:29,240 --> 00:16:31,550
‫So I believe it goes all the way up to here.

210
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‫So it shows us all of the employees that we have in there.

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‫And it even starts a little further up.

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00:16:39,670 --> 00:16:45,190
‫So this is basically the list that we are getting from this for loop.

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‫So you can use a for loop to get through an entire list of dictionaries.

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00:16:50,230 --> 00:16:55,780
‫You can, of course, use A for each loop as well, but you can also access items using element eight

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‫AI and then you can store it and an MP object because the value is going to be in fact off type employee

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‫because that's what we defined here.

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‫Now, if you look at the key, let's run it again.

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‫You can see here, ki seo ki manager.

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00:17:14,090 --> 00:17:15,470
‫Ki h.r.

220
00:17:15,740 --> 00:17:17,000
‫Ki secretary.

221
00:17:17,270 --> 00:17:21,470
‫Now, we could also print the eye if we wanted to.

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00:17:21,500 --> 00:17:22,400
‫So here.

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00:17:24,370 --> 00:17:26,580
‫Like so, Trent.

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00:17:26,710 --> 00:17:29,080
‫Well, actually, let's just print it here.

225
00:17:30,100 --> 00:17:35,320
‫I is and then I will be the second entry like so.

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00:17:35,560 --> 00:17:38,020
‫And then we print I.

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00:17:38,870 --> 00:17:39,190
‫Okay.

228
00:17:39,200 --> 00:17:44,690
‫So then you can directly see which integer value is assigned to a specific position.

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00:17:44,690 --> 00:17:46,670
‫So the CEO is a position zero.

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00:17:46,700 --> 00:17:52,730
‫The manager is at position one, the HR person is a position two and so forth.

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00:17:52,820 --> 00:17:53,370
‫Okay.

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00:17:54,170 --> 00:17:54,590
‫All right.

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‫So that's it for this video.

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00:17:55,730 --> 00:18:00,140
‫I think it's a long enough video to go over dictionaries, at least at this point.

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‫So in the next video, we're going to look at how we can update an existing dictionary, so how we can

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‫update the value of a dictionary and then also see how we can remove data from a dictionary.

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‫So see you in the next video.