# SKB – Scala List Flatten

## Introduction

Periodically, I will publish new exercises so you can slowly build up knowledge about Scala.

It is designed to be done in a very short amount of time and learn a little bit each day, just to create a routine.

This episode will teach you about Scala List `flatten`.

Hope you are going to enjoy it! It is designed for anyone to learn Scala from scratch and slowly learn, one Bit at a time.

After this Bit, I would love to hear your feedback in the comments down below.

Feel free to join the Discord server as well if you would like some help and support from the rest of our community.

## What are we learning today?

Today we are going to learn about Scala List `flatten` !

Do you remember the `map`, from few SKBs ago ?

As a reminder, `map` allows you to transform a `List[A]` into a `List[B]`.

What will happen if `B` is a `List` as well ?

Time to try on the exercise on your own and scroll down for more information when you are done or if you are stuck.

## Exercise

Here is an exercise to complete today.

If I did my job well, you should be able to guess by yourself the solution based on what you previously learned and based on the clues.

The goal of the exercise is to replace the `???` by a piece of code so that the exercise compiles and that’s how you win! Good luck!

You can fill the exercise right in here:

Or, if it does not load, go on to Scastie (fGhtslb9TiiTQ5brcXpgLg).

## More information about Scala List `flatten`

In this exercise you will learn (or have learned, if you have already solved the puzzle) about Scala List `flatten`.

`flatten` allows you to turn a `List[List[A]]` into a `List[A]`.

Try to experiment with other containers such as `Option` we saw in the past.

What happen if you do

```val a: Option[Int] = Some(12)

val aa: Option[Option[Int]] = a.map(x => Some(x))

val flattenA: Option[Int] = aa.flatten
```

Feel free to go back to the exercise, modify the code to try out new things and get a better intuition for Scala List `flatten`.

## Conclusion

I hope you have learned something new or had fun during this Scala Knowledge Bit.

Feel free to try on the next Scala Knowledege Bit.

If you are curious about the previous Scala knowledge Bits, go check it out! 🙂

### 2 thoughts on “SKB – Scala List Flatten”

1. flatten is indeed an interesting topic – one cool thing is that flatMap is just map followed by flatten, i.e. (ma flatMap f) == (ma map f flatten)