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Multidimensional Arrays
7:25Let's explore two dimensional arrays. An array of arrays. Rows and Columns.
Let's talk about multi-dimensional arrays.
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They sound kinda out there, don't they?
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Like science-fictiony or time-travely.
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Well, don't let the name make it
more difficult than it needs to be.
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We're going to explore
two-dimensional arrays,
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or 2D arrays,
which is really just an array of arrays.
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Now the arrays that we've been working
with have been one-dimensional.
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Now 2D arrays are super handy at helping
to describe things in rows and columns.
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If you've used a spreadsheet before, you
can definitely imagine this sort of thing.
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In fact, why don't we just start there?
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So here I've created some golf
score cards using a Google sheet.
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And you can see that I have three score
cards here for each of my friends, Ben,
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Alena, and Pasan.
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They were the same ones at the movies,
we do everything together.
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So these are rows, right?
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Each one of these is a row,
and this is a column, right?
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So this is a column.
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And if I wanna talk about a specific one
of those cells, I can reference it, right?
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So this one here, you can see is B2, and
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this one here is B3, and C3, right?
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Now as we saw with our Ben score card
array, we were able to represent this row,
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Ben's row here, we were able
to represent this as an array.
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But what we're getting at is that
we wanna have these other two cards
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in the same array.
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So now what we wanna do is we wanna
make a new array that has all of this,
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it's gonna have all of these,
each entry is an array.
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So, let's turn this
spreadsheet into an array.
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In the teacher's notes, I've pasted
each of these rows as an array literal.
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I wanna show you how to create this and
then I want to explore it a bit.
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So, first let get it into JShell so
we can play with it.
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But I don't know about you,
but I make mistakes.
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So, one nice trick when making multiple
line statement in JShell just to create
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a temporary file and
then have JShell read it.
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Here, let me show you.
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So, in our workspace,
I am gonna create a new file, and
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I'm just gonna call it scratch.java.
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And we'll use this as
the scratch pad of sorts,
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right, whenever we want
to import things here.
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So, let's define our array.
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You just declare a normal integer array
and remember we want an array of those.
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So you just make one more.
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And then we'll name it scoreCards,
so scoreCards.
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And then we create our
first array literal.
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So we'll say that, and
this is an array, and
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now our array is going to
contain arrays of integers.
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So, let's copy and past Ben's score
card from the teacher's notes.
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So I'm gonna do that and paste Ben's note,
and I'm gonna add a comma,
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cuz that's the first row, and
then I'm gonna add Alena's.
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And I'm gonna add a comma.
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And then I'm going to add Pasan's.
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And now if we bring our spreadsheet
over here and we look at it,
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we have just the same thing.
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So we have 1, 2, 4, 2 for Ben,
1, 2, 4, 2 then for Alena,
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we have 2, 3, 5, 1 and we have 2, 3, 5, 1.
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Cool, and Pasan's 4, 4, 2,
1, 4, 4, 2, 1, awesome.
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So now let's get this
imported in the JShell.
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So we have a file here,
it's called scratch server, saved it,
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also I'm gonna go ahead, I wanna put
a semicolon there as a good citizen.
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And I'm gonna run jshell.
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Bring this up a bit here.
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I'm gonna say /open scratch.java.
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And what that does is it runs
this file and it's now available.
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So now I have a variable
called scoreCards.
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And you'll see that here it is,
it's a multidimensional array,
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the first one is 3 cuz there's three rows
and each one of the rows has 18 columns.
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And remember it really just is
an array of arrays, right, so
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if I look at scoreCards.length, We'll see
that it's 3, that's the number of rows.
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So, to get the first row we just use
index 0, cuz array is a zero based.
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So we'll say score, I'll Ctrl+L here, and
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we'll say scoreCards[0], and there we go.
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It's the first row.
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So this was Ben's score that we pasted,
right?
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So this is Ben's, this is the first one.
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This was Ben, and
the second one here is Alena.
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So let's see how she
did on the fourth hole.
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So that would be
scoreCards[1] to get Alena.
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And then we wanna get the fourth hole,
which again,
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because we're zero-based here too,
would be the third index, right?
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So we'd say [3].
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So right cuz it's for
zero, one, two, three.
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So we get,
awesome a hole in one nice job Alena.
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So now you do that.
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Let's see, I want you to do this as
show me what Pasan got on the 15th hole.
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Remember this is Pasan here.
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So go ahead and access that, and
just print it out here in JShell.
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Go ahead, pause me.
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Did you get it?
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So Pasan happens to be
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The third row which is index 2 and I want
the 15th hole, so I need to subtract 1
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from that to get 14 because both
of those are zero-based, right?
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8, come on buddy, keep practicing man,
you'll get better at this golfing,
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don't worry Pasan.
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I know, let's do this.
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Since we have two arrays, the friends
array and the scoreCards array,
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why don't we loop and
print out all their scores?
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Why don't we take a quick break and
let this sink in a bit.
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Now, taking breaks is a super important
habit to get into for learning.
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So, why don't you take a stretch and
get some fresh air.
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While you're out, let your brain
wonder about 2D arrays a bit.
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Think about how they're just like
the spreadsheet here, right?
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They're just like the spreadsheet
with rows and columns.
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And think about how you can access
them much like, like here is P4,
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this 8 was the same that was row 2,
14, right?
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For it to get to Pasan, 2, 14.
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It's very similar, right?
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One thing that I wanna point out before I
let you go here, you can also add another
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dimension to get a 3D array, but
you have to wear glasses to see it.
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Just kidding.
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But seriously, you can keep appending
them out as far as you'd like, but
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it gets weird quick.
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So when you come back,
we'll loop over our score card.
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Sound good?
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See you in a bit.
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