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In this video we will learn how to implement maps and tuples in Scala. Maps or hash tables are collections of key value pairs. Tuples are an immutable sequence of values and are used for aggregating values.
New Terms:
Map -- Maps or hash tables are collections of key value pairs.
Tuple -- A Scala class which contains collections of different type of elements
Further Reading:
Maps
Tuples
Map documentation & methods
Tuple3 documentation & methods
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Hi, in this video we'll learn how to
implement maps and tuples in Scala.
0:00
Maps or hash tables are collections
of key value pairs.
0:05
Tuples, on the other hand,
are an immutable sequence of values.
0:10
They are also quite useful for
aggregating values.
0:13
Let's get a better idea on these
topics by implementing some examples.
0:17
Similar to previous videos, Scala
collections can be mutable or immutable.
0:22
By default, when we construct
the map in Scala it'll be immutable.
0:27
Let's see how that works syntactically.
0:32
First, let's clean up our
superheros object and
0:35
remove anything associated to lists or
list buffers.
0:38
Awesome.
1:14
We have created a map of type string and
1:14
integer with the superhero name and
ranking.
1:17
Next, let's see how we can
access values in our map.
1:21
Similar to Java,
except without using the get keyword,
1:34
we look up values in a map using
parenthesis and passing in the key.
1:37
And in this case we'll
return a ranking of ten.
1:42
You may have noticed that
the key is case sensitive, and
1:45
it is possible that the key we are looking
for is either misspelled or doesn't exist.
1:49
For instance.
1:54
This will throw a no such element
exception because the key is now found and
2:03
it'll crash our program.
2:07
Let's recompile and run our app.
2:10
As expected, we get a no such element
exception that crashes our app.
2:13
It is considered good practice to
use a method called getOrElse,
2:18
which will return the value
if the map contains the key.
2:22
Otherwise, it will return a default value.
2:26
Let's take a look.
2:28
In this example, the code will
either return the value of the key,
2:39
ironMan, or zero if it is not found.
2:44
But now our program is safe from the key
not found exception and won't crash.
2:46
Additionally, we can
retrieve out the keys and
2:51
values over our map using .keys and
.values respectively.
2:56
Awesome, as we can see, the .keys method
returns a set which is a collection that
3:13
we'll discuss in the next video.
3:18
Meanwhile, the .values returns a map-like
collection with the values of our keys.
3:20
Great, we learned how to create HashMaps,
let's take a look at how to traverse them.
3:26
The following loop construct
allows us to iterate
3:31
over all the key value pairs in the map.
3:34
Lets print out the key value
pairs of our Avengers map.
3:37
Great, if we're only
interested in the values,
3:58
we can loop through avengers.values.
4:01
Let's recompile and run our app.
4:14
Awesome, so far we've only
implemented the mutable map.
4:17
Let's construct a mutable map and
see how we can use it to update values and
4:22
extend our map.
4:26
Let's import the scala.collections
package at the top of our file and
4:28
create a mutable map.
4:34
Awesome, this creates a mutable
map of type string and integer.
5:13
Now we can update the contents of the map.
5:18
Let's up Iron Man's ranking as
Tony Stark's new invention makes him much,
5:20
much stronger.
5:25
Now we can also add a key value
pair to a map using the += method
5:35
Additionally, to remove an element
we can use the -= method and
5:49
pass the key of the element
we would like to remove.
5:53
Let's take a look.
5:57
Great, let's comment out some of our
previous print line statements and
6:04
recompile our app.
6:08
As expected, we've changed the ranking
on Iron Man, we've added Hawkeye, and
6:32
we also removed
Captain America from our map.
6:37
Awesome, we now have a really good
understanding of how maps work.
6:41
In Scala,
6:45
tuples are very easily created by
providing values enclosed in parentheses.
6:46
Let's switch back into our code and
create some tuples.
6:51
In this example, we've created a tuple
three instance with the types string,
7:15
string, and char.
7:19
Tuples in Scala are actually classes
that contain a collection of elements.
7:21
Scala only supports up to tuple 22.
7:26
Which means that we can only have
up to 22 elements in a tuple.
7:29
Unlike some of the other collections we
saw, tuples are not zero index space, but
7:34
rather they start at one.
7:38
Accessing the first element
in a tuple can be done
7:40
with an underscore followed
by the index value.
7:43
Let's take a look.
7:46
Let's recompile and run our app.
8:11
Awesome, we were able to retrieve
Hawkeye's name and also his birthplace.
8:18
To loop through the elements in a tuple,
8:23
we have to use a method
called product iterator.
8:25
Great, let's recompile our app and
check out our results.
8:39
As expected, we've printed out the name,
birthplace and gender of Hawkeye.
8:44
Awesome, we learned what maps and tuples
are and how to perform operations on them.
8:50
In the next video, we will learn about
another data structure called sets.
8:55
See you there.
9:00
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