zip.scala

// zip3 Lists
object ZipUtils {
  def zip3[A, B, C] (xs: List[A], ys: List[B], zs: List[C]) : List[(A, B, C)] = {
    def zip3_aux(xs: List[A], ys: List[B], zs: List[C],
                 acc: List[(A, B, C)]) : List[(A, B, C)] = (xs, ys, zs) match {
      case (xh :: xt, yh :: yt, zh :: zt) => zip3_aux (xt, yt, zt, (xh, yh, zh) :: acc )
      case _ => acc.reverse
    }
    zip3_aux(xs, ys, zs, Nil)
  }

  def zipWith [A,B,C] (f: (A, B) => C) (xs: List[A], ys: List[B]) : List[C] = {
    xs zip ys map { case (x, y) => f(x, y) }
  }

  // zip3 Vectors
  def zip3[A, B, C] (xs: Vector[A], ys: Vector[B], zs: Vector[C]) : Vector[(A, B, C)] = {
    val l = xs.length min ys.length min zs.length
    def zipaux (v: Int, acc: Vector[(A, B, C)]) : Vector[(A, B, C)] =
        if (v == 0) acc
        else zipaux(v - 1, acc :+ ( xs(l - v), ys(l - v), zs(l - v) ))

    zipaux (l, Vector.empty)
  }
}