Preview
Video Player
00:00
00:00
Ruby Hash Creation
6:35Let's start working with hashes now. Hashes are created in a couple of different ways. A hash can be instantiated using curly braces or instantiating a new instance of the class.
[MUSIC]
0:00
In Ruby, a hash is similar to an array.
0:04
Both arrays and hashes allow us
to store different things and
0:08
multiple different kinds of things.
0:12
Hashes are a little bit
different than arrays though.
0:15
In an array we can only refer to
an item based upon its position or
0:18
index in the array.
0:24
Inside of a hash, we use an identifier to
describe the item that we wanna access.
0:26
The identifier can be
almost any Ruby type,
0:32
but the most common are strings,
numbers, and symbols.
0:35
Let's take our grocery list
example from earlier and
0:41
say that we wanted to store the number of
items we wanted to buy on our grocery list
0:44
along with the list itself.
0:48
We could use a hash for that and say we
store the item, which would be bread,
0:51
and the quantity of one.
0:55
When we refer to the items in a hash, the
identifier that we use is called the key.
0:57
And what we store there
is called the value.
1:04
In this case, the item would be one key,
and bread, the value.
1:08
Quantity is also a key, and
one would be the value there.
1:13
We write hashes similarly
to how we write arrays.
1:19
Let's create a hash now using WorkSpaces.
1:23
Okay, so I've just launched a new Ruby
workspace, and let's go ahead and
1:27
launch irb and
see how we work with hashes.
1:31
Now with arrays we were
creating our grocery list.
1:36
Now let's concentrate on
individual grocery list items.
1:39
So we'll say the item is a new hash.
1:44
Now we write that out just like we
did with arrays by saying Hash,
1:47
with a capital H, a dot and new.
1:52
Now, just like arrays,
we also have a shortcut for
1:56
creating a hash,
which is going to be the curly braces.
2:01
And we have an opening curly brace,
and a closing curly brace.
2:05
Now we can see that Ruby returns this,
and that is an empty hash.
2:11
But empty hashes are no fun, so let's go
ahead and create our grocery list item.
2:16
And we'll say the name is bread, and
here we've created our first hash.
2:22
Now I've done this by separating
the curly brace with a space.
2:29
That is totally optional.
2:34
Now the way that we do this, in this
instance, name here is a string, and
2:37
that is the key, and bread is also
a string, and that is the value.
2:41
So name is the key, bread is the value.
2:50
So if we wanted to find out
the value at the hash key of name,
2:54
we would type in the name of the hash,
which is item, and then opening brackets
2:59
just like we accessed arrays, and
then the key that we wanna retrieve,
3:04
which in this case is name, and that
will return the value, which is bread.
3:08
Now we can create hashes with
more than one hash key and value.
3:15
We can say name is bread, and
since this is a grocery list,
3:20
maybe we would want to buy more
than one loaf of bread, and
3:25
we could say, we could do a quantity of 1.
3:29
And that will return our hash,
3:33
now it has two keys, one being name,
the other being quantity.
3:37
And values, bread and
1, which is a number.
3:41
Hash keys can be almost any Ruby type or
object, and so could hash values as well.
3:46
Hash keys, let's go ahead and create one,
we'll just say, we'll use a number here,
3:54
so 1, that could be a grocery store.
3:59
Doesn't actually mean anything, but
if we look back at our hash now,
4:03
we have added the key of 1 with
the value of grocery store.
4:07
Doesn't quite make sense in this context.
4:12
Just wanted you to see that you
could use a number as a hash key.
4:14
And let's go ahead and
add another key here.
4:21
And we can add a key to an existing
hash by typing the name of the hash,
4:23
opening the bracket, and
then the name of the new key.
4:29
And we'll say the brand
of bread that we want.
4:33
And then we assign this
like any other value, so
4:36
I'll say Treehouse Bread Company, and
that will create a new key in the hash.
4:40
Let me clear my screen here so
we can see it a little better.
4:47
And the name is bread, quantity of 1,
and our miscellaneous key of one,
4:49
which is a grocery store, and
the brand is Treehouse Bread Company.
4:54
Another way that you might see
keys written is with symbols.
4:59
A symbol is just like a string except
it's written with a colon in front of it.
5:04
And so let's just say the item
with the name of bread.
5:11
Now if we look at our item hash.
5:16
We have another key here name
with the value of bread,
5:18
and this has a colon in front of it.
5:24
The only difference between these
two is that in Ruby's memory
5:26
there will only be one symbol called name,
5:31
whereas each time we use a string
there's a new one inside of the memory.
5:35
And we don't really need to worry
about that too much right now but
5:40
if you see that you will occasionally see
5:43
hash notation with symbols as hash
keys instead of strings or numbers.
5:46
Now let's go ahead and
get one out of there.
5:52
We could say delete and that will
return the item at the given hash key.
5:55
And now here we go.
5:59
We've got our hash with the name of bread,
and
6:00
the symbol, also with the name of bread.
6:04
Now, when we're creating a hash, if we
wanted to just use symbols as hash keys,
6:07
you could do it like this.
6:12
And in that case we don't have to
use the equal sign and the arrow.
6:17
And if we look at our hash, it will be
just the same as if we were using symbols
6:22
as keys and anything else as the value.
6:26
Try creating some hashes on
your own now using WorkSpaces.
6:30