Convert List of 1 element to Option

Question

Let's say I have a List[T] from which I need a single element, and I'd like to convert it to an Option.

val list = List(1,2,3)
list.take(1).find(_=>true) // Some(1)

val empty = List.empty
empty.take(1).find(_=>true) // None

This would appear to be somewhat of a hack ;-)

What's a better approach to converting a single element List to an Option?

When you have doubts like that it could be useful to look at http://scalex.org/ as well. It's kind of type search for scala, similar to haskell's hoogle. You just type signature of function which you are looking for and it tries to find every function which could match. In this case just try 'List[A] => Option[A]' and you will see headOption as second result. — Piotr Kukielka, Oct 31 '13 at 09:52

score 26 · Accepted Answer · answered Oct 30 '13 at 18:37

26

Scala provides a headOption method that does exactly what you want:

scala> List(1).headOption
res0: Option[Int] = Some(1)

scala> List().headOption
res1: Option[Nothing] = None

answered Oct 30 '13 at 18:37

wingedsubmariner

and `toList` applied to an `Option` is the inverse of it – matanster Apr 16 '16 at 10:29

score 16 · Answer 2 · answered Oct 30 '13 at 18:37

16

headOption is what you need:

scala> List.empty.headOption
res0: Option[Nothing] = None

scala> List(1,2,3).take(1).headOption
res1: Option[Int] = Some(1)

answered Oct 30 '13 at 18:37

@virtualeyes Please accept winwingedsubmariner's answer as his answer seems to be 10 seconds ahead. I will delete mine. – Marimuthu Madasamy Oct 30 '13 at 20:03
done, although, you should both get credit, essentially answered at the same time – virtualeyes Oct 30 '13 at 20:43

2 Answers2