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),         


        

Answer 1

Here's a slightly cleaner one:

def groupConsequtive[A](list: List[A]): List[List[A]] = list match {
  case head :: tail =>
    val (t1, t2) = tail.span(_ == head)
    (head :: t1) :: groupConsequtive(t2)
  case _ => Nil  
}

tail-recursive version

@tailrec
def groupConsequtive[A](list: List[A], acc: List[List[A]] = Nil): List[List[A]] = list match {
  case head :: tail =>
    val (t1, t2) = tail.span(_ == head)
    groupConsequtive(t2, acc :+ (head :: t1))
  case _ => acc
}