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So will come back again in this lesson we're going to continue with the collections in Objective C and

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we will be talking about a particular type of collection called a dictionary.

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Dictionaries are essentially a key value pairs collection.

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What it means is imagine if you have an array and then every element in the array.

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So of having an index that has a numeric value it has an actual title that you can search for that title

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and find that a specific item in your array.

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The action is essentially the same thing that they allow you to have a key value pair or objects within

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a collection.

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So that's going to ex-cult next for them when I close this project I'm going to start a new one say

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command line tool.

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This is dictionaries project so you know dictionaries project on regular started with my very first

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dictionary.

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So let me get some better formatting in here as usual.

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And then the first thing I'm going to do is that I'm going to say I have a..

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Dictionary.

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This is going to be my first dictionary that's going to be and this dictionary dictionary it up just

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for me.

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So I'm going to say the opposite that I have.

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It's going to be my name and the key for it is going to be name G or anything like that.

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So right now I have a dictionary vaire an object that is content.

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This here is associated with a key called the name key.

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So if I want to find out I could go ahead and say and Aslaug let's say a value for name is and whatever

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object you find the later on and that value is going to be my first dictionary object for key and the

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object for a key is the key I'm looking for is name me.

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Let's run this or this project is going to do it is going to say let's go to my first dictionary search

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for a key and that key is Name Key and find the value for it.

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I'm printed in here.

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Now keep in mind that the keys are arbitrary values they don't have to be anything specific if you want

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call this in.

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And obviously when you're searching the search for a name if you want to call it name then you know

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call that one name and this one name.

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I usually tend to finish them with a tidy key so I know that these are my keys.

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And the other ones are my values.

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Now while this might be useful it's very difficult to enter values like this.

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So instead of having a dictionary with a set number of ideas they actually usually make this mutable

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dictionary and be cheap.

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Adding values to it.

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Let's see how we're going to do that.

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So now I'm going to say and it's mutable dictionary.

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This is going to be my mutable dictionary that's going to be and that's mutable dictionary oarlock and

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in it it is allocated on initialize.

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So now there is a mutable dictionary.

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It is declared it is located initialize and it can take in values such as what I would say might mean

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a dictionary are a set value and the value is going to be my name for the key name key and then I'm

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going to say again my mutable my mutable dictionary sets a value and the value is Vancouver and set

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for a city XI.

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And let's have one more my mutable dictionary and sets a value and this value is going to be I guess

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on this one is going to be force Name Key.

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So now I have a dictionary that has three different keys and each key obviously has a certain value.

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And if I want to find any of those I could simply go ahead and say let me copy the entire thing our

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name or use is for instance name of use he is under I would say my immutable dictionary object for key

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on the name key.

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I have to make sure that the keys I use are existing in here.

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Otherwise there won't be any result.

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It will then give me an error or it just wouldn't print anything.

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So let's bring that out.

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Purrfect that's the first one in here.

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And this is the second one.

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Let's print the city of the city of that is for city key.

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Perfect Now as you can imagine in a larger dictionary such as this one there is 3-D Frenchy's and there

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are also to different values you could actually access those and put them in an array so I could say

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and Aslaug on a cheese bar and then whatever you find in my mutable dictionary all cheese.

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So what is going to do is going to actually produce all of the kids put them in an array.

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And then it's going to print them for me.

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And the reason I know it's going to be an array is that because when I write all the keys it tells me

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it's not all in this array it's going to return and it's way for me.

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So all keys.

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And similarly I could do the same thing for all the values I'm going to say or the values or values

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or run this so what we have done here is you obviously have the two prints that you had before.

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A nice thing.

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All keys are our main city of course Name Key and then all the values are in Vancouver.

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I was just like what we expect.

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Now if for any reason you don't want to use a mutable dictionary and you want to define and declare

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everything in one go you could actually do without us.

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So I could go ahead and say r and s dictionary are.

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Let's call this one multiply.

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You use the dictionary is in this dictionary dictionary.

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The last time we use a dictionary with object for key.

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Now this time I'm actually going to use dictionary with objects and keys proof multiple objects and

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multiple keys.

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So the way you write those is like this.

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I'm going to say actually with objects and keys.

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Every first value every first entry will be considered a value on every second one with because a key.

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So essentially right now there is one key called K for one value called the V.

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Now let's try to remake this thing that we have up there.

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I'm going to say it is a mere The name key and it's a good practice to actually not bring this one line

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down so we can see them properly next to each other.

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And then I'm going to say the next one is code word for City Name Key and then I think the last one

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with the I O S on this with the horse name keep perfect.

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So this is not a dictionary that the initialization Lebaran initialising you're putting up multiple

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values in it.

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So this is one key value.

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This is another key value and this is another key value.

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And just like the previous examples I could just go ahead and say print a certain thing from here say

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and I like my R value for either no.

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Of course he is.

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And then when I say on and then I'm going to say multiple values dictionary object for key and the key

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I'm looking for is horse name Keith.

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That's wrong and if it all goes well it should print.

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I was at the very end.

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Yes value for course is I always know that because the sense of how dictionaries are built we have to

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talk about something quite important that is missing dictionaries within arrays or arrays within dictionaries.

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So to do that I'm actually going to comment out all of my N.S. logs so we don't see a lot of stuff here.

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I'm going to go ahead and say Karmen this one out.

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Carmen Carmen Carmen.

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And if you're wondering how do I do this common thing is command and forward slash.

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It's a hot key for commenting out anything that is in the current line.

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So if we select these guys and say command forward slash it Carmens all of them out and if they do it

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again it essentially on common stuff.

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So now when we run our application or run successfully What we don't see anything down there because

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we are not printing any values.

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So in this example I want to do this I want to put two users inside one array.

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So once again to use users inside one array and every user has only two entities name and city.

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So just go ahead and do that.

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I'm going to say N.S. dictionary use.

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One dictionary is going to be an ass dictionary dictionary.

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Objects and keys and the objects are these.

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And you know that his name key just like what they have done before.

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I have the other user which is the other piece of information which is Vancouver and that is for a city

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or city she and that's one of my users.

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Let's duplicate this once again.

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And the copy I'm going to say use to dictionary this is going to be Steve.

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Steve lives in either North San Francisco.

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If that's how you spell it so good.

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Two dictionaries each of them about one of my users.

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And now I want to put both of them inside an array.

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So I'm going to say and this mutable array Let's call this one user's array.

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Is this N.S. mutable array lock and in it.

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And that's not a bad time to mention this whenever you have to do this.

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I look in it.

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You can do only one and that is new.

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So this is a lot in it I could say just do you.

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Which is exactly identical to saying aloud and then saying in it.

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So this too would be exactly identical.

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So let's move to our users array and I'm going to say use as array as the object.

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Use one dictionary.

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And then I'm going to say use array and object and now add the user to dictionary.

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So most of my dictionaries are now added inside my array and if I print my array and log whatever object

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you find in the user's array.

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If you print this we should be able to see the entire thing in one big array.

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So just like Will we expect that this is the array.

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So that is the array that you Panthers these are the two round brackets.

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Within that there is one object column or the other object.

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And as we expected within that curly brackets which is our dictionary there is the city of Vancouver

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named Amir.

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And then for the other use the city key sanfrancisco name key Steve.

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Now in the next few lessons when we talk about flu we will learn how to search between all of these

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elements and find exactly what we want.

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But for now I just want to show you something real quick.

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Imagine we wanted to go and find our second array object in the array and from that we wanted to get

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the name of the user.

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So I'm going to say name of their second are our dictionary.

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Does the name here I would say on one line down I would say use Array object that index 1 that is the

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second one.

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Remember arrays start from 0 0 1.

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So now we got that first dictionary.

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Then I'm going to open another bracket and then close up and say object for CI and they keep I'm looking

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for is name key.

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So it's essentially saying if you wanted to see it visually is saying go to the user's array in the

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users or go to the object that index one or not to this one but this one in here says one object for

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the key name key and that's the name key.

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Are printed.

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So let's see what we get.

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Run that I sing name off the second dictionary is Steve or a dad naming name for the second use I should

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have said so I can use a name for this I can use that is Steve.

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Just like how you expected it to be.

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So that's about that.

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Dictionaries are of value key pair collections.

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You can have so many different keys and so many different values inside the dictionary to find a certain

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value within a certain dictionary.

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We look for object for key.

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We get that we can also get things such as all the keys and we can get all the values there is more

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of these methods such as getting all the values for a certain key or getting all the kids that correspond

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to this value.

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What are those things where can see them as we go along and we actually you know use dictionaries inside

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our applications.

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For now just learn how to essentially initialize dictionaries either with a single key value pair or

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with a mutable matter that you can keep adding new values to them or with multiple values in one go.

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Obviously about nesting in different dictionaries inside an array which is a very common practice.

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And of course finding values inside them getting the array from the array.

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Getting that particular object that is a dictionary.

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And from that dictionary getting the object for a particular cheat would be essentially what you would

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need to do.

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So that's about that.

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Let's keep it up to here on in the next lesson.

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We'll move on.

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I treasons on for loops on control froths.