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Hey everybody what's going on this is Caleb with Debb slopes dot com.

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And in this video we're going to start talking about transformations K transformations are ways that

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we can modify and transform data in our swift and thankfully Thanks to our swift being functional it

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allows us to basically take a stream of inputs and run them through a function the outputs of that function

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we can run into another function so on and so forth.

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So we're going to talk about map today.

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Now map is a function and I'm going to show you something now from the developer documentation on Apple

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dot com.

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And the map is a function that returns an array containing the results of mapping a given closure over

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the sequences elements.

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So we can call map on arrays.

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We can also call map on observables K because remember it's a sequence an asynchronous because remember

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an observable is an asynchronous sequence.

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So pretty cool.

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Basically how it works is you can call map on an array or a dictionary actually in Iowa 11 as well but

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you can call map on an array and what it's going to do is inside the map closure.

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Think of it like a for loop.

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It's going to cycle through every element and you can apply some type of transformation to the elements.

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Then once map is finished it returns the array of the updated elements.

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OK that's the cool thing about map.

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So let's go ahead and close this and let's actually learn how it works in real life.

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So pull open your X playground and we're going to right click on our latest playground and create a

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new playground page.

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We're going to call this map.

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All righty.

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Now just like before we're going to need to select all here and delete all of that information and then

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we're going to just copy our three lines that we've been using and paste them in like that.

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All righty.

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So very cool.

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Now let's begin by creating a Dispose bag like so let dispose.

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Bag equals dispose bag.

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Put some parentheses there to instantiate it.

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And we now have a Dispose bag we can use.

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So what we're going to do is we are basically going to create an observable of type and number.

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We're going to give it a few numbers and then we're going to use map to transform all of the elements

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in that sequence into something else.

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So we're going to actually begin by creating a number formatter which is going to take our numbers and

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when we run them through the map closure we're going to transform them from the actual numerical value

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into the textual word or of that number like if instead of the number one we will spell out o and e

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k.

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That's what a number formatters going to let us do.

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So let's create that now by typing let formatter equals number formatter.

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And you're noticing that things showing up.

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We need to import foundation so that we have the foundational elements of swift.

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So go ahead and type import foundation and you'll notice it'll turn blue eventually.

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But now we have access to number four matter.

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Hey let's maybe try building and see if that helps.

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Maybe not maybe go here maybe go back looks like it's not going to let us I'm going to save and quit

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X code here pull it back open and let's open that back up again.

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And here we go.

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There we go.

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So now you can tell that it's properly instantiated and we need to set the number style now because

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this is a format so it can help us change the style so type formatter number style.

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And we can use the enumeration number style basically to pull out spell out k specifies a spell out

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format for example one two three four point five six seven eight is represented as one thousand two

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hundred thirty four point five six seven eight.

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That's the cool thing is it spells it out like you would say it.

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That's the format we're going to use.

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So now we're going to create an observable of type and S number and we're going to give it an array

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with three values K because remember map is going to cycle through a sequence so we need to have multiple

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values or well I guess with an observable can be 0 or more values just because it's an observable it's.

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It's counted as a sequence or an array which is why it works with map.

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So go ahead and type observable of type with the brackets they're of type and as number k and we're

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going to use our DOT of function.

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OK.

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Now Dot of like you saw here of says creates a new observable instance with a variable number of elements

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meaning we can include as many as we want.

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So let's include just a couple of numbers here maybe 123 maybe 47 and maybe 9.

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OK.

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So we now have an observable of type and a number and it has three values inside of it.

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It's a sequence of three at the moment.

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Now what we can do is we can call dot map and it says that it projects each element of an observable

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sequence into a new form.

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So it's going to allow us to map those values onto a new form.

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So go ahead and type map and instead of pressing enter and using the closure here what we can do is

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we can simply press space and put two brackets k that will work the same exact way.

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So it's just kind of a shortcut there.

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Now I'll show you something in a second we're going to fix it now in our X Swift.

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What is common is after the declaration to go before the period there and press enter and what it's

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going to do is it's basically going to put all of our functions kind of indented underneath this observable

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and it'll still work the same exact way.

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It's just a little bit indented and a little more easy to read the flow of events because remember it's

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a synchronous it goes from top to bottom.

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So now that we are in our map this is sort of like our for loop if we had like four number in observable

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and that's number whatever it would cycle through and we could modify that number principle for each

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value.

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But instead what we're going to do is inside map we're going to call formatter dot and we're going to

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use the string function.

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OK.

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And it's going to basically take a number and it will turn it into a string so string from an S number.

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And what is the N.S. number that we're going to pass in in our function.

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We can use a temporary variable dollar signs 0 and what it's going to do is it's going to cycle through

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all the numbers that get passed in and it's going to basically pass 123 in the place of dollar signs

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zero.

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Then once that's done it goes back through 47 gets passed in here then 9 gets passed in here.

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What this is doing is this is basically the input here 1 2 3 4 7 and 9 those that input gets passed

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into map and then at the end basically map produces a basically map produces a new element right with

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a string value instead of a and s number value.

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What we can do now after we have mapped all the values to turn them into the text based string we can

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call a dot subscribe.

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Do you see how we're sort of chaining these functions together.

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We can call subscribe and then pass on next k just like we have been in previous videos reusing on next

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because as soon as we use one value here we're passing a value here that produces an on next call then

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47 gets passed that produces another on next call and then 9 finally produces the final on next call.

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Now what we are doing here we're using map to create a new array of values.

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And so what we can do is when we go into our subscriber block we're passing in that array so we pass

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in the values here to map K and we go through the map function and then we pass an array of all of our

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new text values into subscribe K.

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What we can do then is we can print dollar signs zero and that's going to print all the values that

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we just passed in look at this.

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One hundred twenty three forty seven nine.

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Ok that's cool.

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It's printing out every value as we go through.

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Then of course at the end once we have subscribed we need to tell it that we need to deallocate the

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memory that it's holding.

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So we can type add two disposable bag or add disposable to bag and we can pass in our dispose bag that

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will handle the memory management for us.

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So like I said before for every dot you want to put it on its own line that just kind of helps to consolidate

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and space it out.

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Now there is an issue though as you can see we are getting an optional value and that's because this

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observable We don't know when the end of it is going to be.

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So we don't want to pass in a nil value and so because of that it comes in as optional.

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But what we can do is we can use the ternary operator to basically set a blank string value if a nil

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value comes in.

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So if this is good it's going to set the value to be the string based value of that number.

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Otherwise we want to return a blank string.

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So go ahead and type two question marks there for the ternary operator basically saying otherwise or

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else we'll pass it a blank string and watch what this changes in the console.

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As you can see it's now printing out a non-optional value of string for each of our numbers.

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That is how map is super super cool.

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We're passing in an observable here.

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We're passing in these three values.

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They're getting formatted and turned into a string and then we can do something with all those values.

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OK.

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That's super cool.

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We can then at the end add it to our dispose bag and the memory is deallocated at exactly the right

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time and we don't even have to think about it.

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This is just one way.

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That map is helpful and map is not a an Arctic swift exclusive feature map is also available in regular

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swift So if you're using a regular Swift and you want to perform a very clean iteration over an array

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and transform all the values.

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This is a really amazing way you could do that.

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So this is map this is how map works especially in ARC swift with observables.

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And we're going to go ahead and move on to the next video where we'll talk about flat map which is similar

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but a little bit different.

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So let's head on over to the next video.

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Awesome job with this one guys and we're really making a lot of progress in understanding based foundational

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arcs Swift.

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Soon we're going to be building apps and really cool projects with it.

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So let's head over to that next video.

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Awesome job guys.