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# R4ncid's solution

## to Flatten Array in the Scala Track

Published at Jun 26 2020 · 0 comments
Instructions
Test suite
Solution

Take a nested list and return a single flattened list with all values except nil/null.

The challenge is to write a function that accepts an arbitrarily-deep nested list-like structure and returns a flattened structure without any nil/null values.

For Example

input: [1,[2,3,null,4],[null],5]

output: [1,2,3,4,5]

The Scala exercises assume an SBT project scheme. The exercise solution source should be placed within the exercise directory/src/main/scala. The exercise unit tests can be found within the exercise directory/src/test/scala.

To run the tests simply run the command `sbt test` in the exercise directory.

Please see the learning and installation pages if you need any help.

## Source

Interview Question https://reference.wolfram.com/language/ref/Flatten.html

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### FlattenArrayTest.scala

``````import org.scalatest.{Matchers, FunSuite}

/** @version 1.2.0 */
class FlattenArrayTest extends FunSuite with Matchers {

test("no nesting") {
FlattenArray.flatten(List(0, 1, 2)) should be(List(0, 1, 2))
}

test("flattens array with just integers present") {
pending
FlattenArray.flatten(List(1, List(2, 3, 4, 5, 6, 7), 8)) should be(
List(1, 2, 3, 4, 5, 6, 7, 8))
}

test("5 level nesting") {
pending
FlattenArray.flatten(List(0,
2,
List(List(2, 3), 8, 100, 4, List(List(List(50)))),
-2)) should be(
List(0, 2, 2, 3, 8, 100, 4, 50, -2))
}

test("6 level nesting") {
pending
FlattenArray.flatten(List(
1,
List(2, List(List(3)), List(4, List(List(5))), 6, 7),
8)) should be(List(1, 2, 3, 4, 5, 6, 7, 8))
}

test("6 level nest list with null values") {
pending
FlattenArray.flatten(
List(0,
2,
List(List(2, 3), 8, List(List(100)), null, List(List(null))),
-2)) should be(List(0, 2, 2, 3, 8, 100, -2))
}

test("all values in nested list are null") {
pending
FlattenArray.flatten(
List(null,
List(List(List(null))),
null,
null,
List(List(null, null), null),
null)) should be(List())
}
}``````
``````object FlattenArray{
def flatten(list:List[Any]):List[Int] = {
def loop(l: List[Any], acc: List[Int]): List[Int] = l match {
case ::(null, tl) => loop(tl, acc)
case Nil => acc
}
loop(list, List())
}
}``````

### What can you learn from this solution?

A huge amount can be learned from reading other peopleâ€™s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

• What compromises have been made?