Scala List function for grouping consecutive identical elements

Question

Given e.g.:

List(5, 2, 3, 3, 3, 5, 5, 3, 3, 2, 2, 2)

I'd like to get to:

List(List(5), List(2), List(3, 3, 3), List(5, 5), List(3, 3), List(2, 2, 2))

I would assume there is a simple List function that does this, but am unable to find it.

Answer 1

This is the trick that I normally use:

def split[T](list: List[T]) : List[List[T]] = list match {
  case Nil => Nil
  case h::t => val segment = list takeWhile {h ==}
    segment :: split(list drop segment.length)
}

Actually... It's not, I usually abstract over the collection type and optimize with tail recursion as well, but wanted to keep the answer simple.

Answer 2

val xs = List(5, 2, 3, 3, 3, 5, 5, 3, 3, 2, 2, 2)

Here's another way.

(List(xs.take(1)) /: xs.tail)((l,r) =>
  if (l.head.head==r) (r :: l.head) :: l.tail else List(r) :: l
).reverseMap(_.reverse)