StreamExamples.scala

package org.examples
 
object StreamExamples {
  // group List(1,1,2,2,2,3,4,4) =>
  //        List(List(1,1), List(2,2,2), List(3), List(4,4))
 
  def group[A](s: Stream[A]): Stream[List[A]] =
    s match {
      case Stream() => Stream.empty
      case hd #:: tl =>
        val (dups, tail) = tl partition (_ == hd)
        (hd :: dups.toList) #:: group(tail)
    }
 
  // group Stream(1,1,2,2,2,3,4,4) =>
  //       Stream(List(1,1), ?)
  //         Stream(List(1,1), List(2,2,2), ?)
  //           Stream(List(1,1), List(2,2,2), List(3), ?)
  //             Stream(List(1,1), List(2,2,2), List(3), List(4))
 
  def testStreamExamples() = {
    val s = group(Stream(1,1,2,2,2,3,4,4))
 
    (s take 1) foreach println
    println(s)                     // Stream(List(1, 1), ?)                          (1)
    (s take 2) foreach println
    println(s)                     // Stream(List(1, 1), List(1, 1), ?)              (2)
    (s take 3) foreach println
    println(s)                     // Stream(List(1, 1), List(2, 2, 2), ?)            (3)
    (s take 4) foreach println
    println(s)                     // Stream(List(1, 1), List(2, 2, 2), List(3), ?)   (4)
  }
}