- Chaining Array Methods 3:37
- Method Chaining 1 objective
- Working with Objects in Arrays 7:40
- Working with Objects 1 objective
- Combining filter() and map() 4:13
- Combining filter() and map() 1 objective
- Combining filter() and reduce() 4:42
- Combining filter() and reduce() 1 objective
- Nested Data and Additional Exploration 7:25
- Array Flattening 1 objective
- Nested Data 1 objective
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Nested Data and Additional Exploration
7:25Work some more advanced array problems using the methods you've learned about in this course.
We're almost to the end with this
introduction to array iteration methods.
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Here's another common array data pattern
I want to prepare you to tackle.
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Sometimes, you can have an array of
arrays, and you need to take the elements
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out of each internal array and
place them in one big array.
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So for example, let's say I had
an array of movie titles, and
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I wanted to have all the movie
titles in one big array.
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This is commonly called flattening because
you're putting the internal elements
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all on one level.
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In this case,
we want to end up with an array, but
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it will be a different kind
of array than we have.
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Because we have arrays,
but we want strings.
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Map won't work for this because one way or
another, we'd still end up with
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just three elements, and
we need each title to be its own element.
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Because we want to fundamentally alter
the array structure, we can use reduce to
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collect the internal array elements and
place them in a new array.
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I'll show you how.
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First, I'll declare a variable
to capture the new array.
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Then I need to call reduce
on the movies array.
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For the callback,
I want the accumulator to be a new array.
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And I'll name each array item innerMovies.
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I want to set a new empty array for
the first iteration.
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Inside the callback, I pull the array
elements out of innerMovies,
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which are the strings themselves,
and place them in the accumulator.
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I could do this a number of ways.
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Arrays have a concat method for example,
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that I could use to concatenate the inner
movies array onto the accumulator array.
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Look for
details on concat in the teacher's notes.
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I'm going to use the spread operator,
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which places the elements of
an array into another array.
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If the spread operator is new to you,
check out the teachers notes for
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more information about them.
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Because we have two arrays that we
want to join, I'll return a new
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array that starts with the all the
elements collected inside the accumulator.
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And ends with all the elements
from innerMovies.
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And then I will log this to the console.
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I'll save it and run iteration.js.
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And, movies.array.
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I want reduce not array.
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I'll save that.
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Clear and run it.
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And you can see we have
an array of strings now.
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Let me show you how to use
this on a larger example.
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Let's take our users
from an earlier video.
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What if each user wanted to
track their favorite books,
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which were kept in a user object?
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Something like this.
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You can copy this from the snippets in
the teacher's notes below if you want to.
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Let's say we want to create an array of
all the favorite titles from every user.
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To do this, we need to iterate
over the array of customers.
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And in each customer, iterate over the
favorite books array, pulling out titles.
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Let's walk through how
to tackle this problem.
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If you want to pause now and
try to work it on your own, please do.
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While we just worked with an array of
arrays, now we have an array of objects.
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Each object contains an array of objects.
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As with many of these problems,
this could be solved a number of ways.
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I'll take the approach of
simplifying this structure first,
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then applying the flattening
technique you just learned.
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I'll map over the outer array, and
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inside I'll map again to
create an array of arrays.
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Let me show you what I mean.
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I'll start by creating a variable, books.
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And I'll map over the users array.
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And I'll put map on its own line.
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In the body of the callback,
we want to return an array of book titles.
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We can do that by mapping over
the favoriteBooks array, and
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returning the titles.
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The inner call to map returns
an array of strings and
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the outer call to map returns
an array of those string arrays.
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So we can now reduce over
this array to flatten it.
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I'll add reduce to the chain, and
build up the array of strings,
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the same way we did earlier.
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And I'll log books to the console.
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And save and run this file.
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You can see we get our array of strings.
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You'll find that the more
you work with these methods,
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the more useful they'll become.
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You can start with a practice
right after this video.
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But first, let me show you how
to find more information about
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the methods we covered as
well as other methods.
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Let's go to the MDN page for arrays.
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On the left, you can see all
the array methods listed together.
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But if I expand this index,
you can click on iteration methods.
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And that'll bring up all the array methods
we've covered as well as some other ones.
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>> Let's click on every, for example.
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>> This method lets you check whether
all elements meet a certain condition.
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It returns a Boolean value.
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Basically, this method asks if every
element meets the supplied condition, and
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returns true if so and false if not.
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Thank you for
exploring array iteration methods with me.
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I hope you had fun learning about them,
and
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that you feel comfortable practicing them,
and using them on your own from here.
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They're powerful tools that give
you a lot of control to wrangle and
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digest array based data.
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I hope to see you soon in a later course.
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Til then, have fun coding!
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