Some generators for choices, permutations, shuffling, etc.

Comb.scala

import scalaprops._

/** Generate a permutation of the given values.
  *
  * > permute("ABC").sample
  * Vector(A,C,B)
  * > permute("ABC").sample
  * Vector(B,A,C)
  */
def permute[A](values: IndexedSeq[A]): Gen[IndexedSeq[A]] =
  for {
    selections <- permutation(values.size)
  } yield selections.toIndexedSeq.map(n => values(n))

/** Generate a permutation of `size` elements.
  *
  * > permutation(3).sample
  * Seq(1,2,3)
  * > permutation(3).sample
  * Seq(3,1,2)
  */
def permutation(size: Int): Gen[Seq[Int]] =
  selection(size, size)

/** Generate a selection of `choose` items from `available` options.
  *
  * > selection(5, 3).sample
  * Seq(4,1,2)
  * > selection(5, 2).sample
  * Seq(1,4)
  */
def selection(available: Int, choose: Int): Gen[Seq[Int]] =
  for {
    keys <- Gen.sequenceNList(available, Gen[Double]).map(_.toSeq)
    selections = keys.zip(1 to available).sortBy(_._1).map(_._2)
  } yield selections.take(choose)