Beam over permutations, find the best possible sequence given a perplexity function

beamPermute.scala

def beamPermute[T](
  data:         List[T],
  perplexityFn: List[T] => Double,
  startNode:    T,
  beamSize:     Int               = 10,
  beamWindow:   Int               = 3
): List[(List[T], Double)] = {

  var candidates = List((List(startNode), 0d))

  // var leftOver = data.to[ListBuffer]
  data.foreach{ _ =>

    candidates = candidates.map{
      case (c:List[T], p:Double) =>
        var now = data.to[ListBuffer]
        c.foreach{ x => now -= x }

        now.map{ d =>
          val x = (c :+ d).takeRight(beamWindow)
          ((c :+ d), perplexityFn(x))
        }
    }.toList.flatten
      .sortBy{ x => -x._2 }
      .take(beamSize)

  }

  candidates
}

def beamTest:Unit = {
  val testData = List("999999999", "22", "55555", "333", "666666", "4444", "7777777", "88888888")

  val res = beamPermute[String](
    testData,
    (x:List[String]) => x.mkString(" ").length.toDouble, 
    "1",
    beamSize=testData.length, 
    beamWindow=testData.length
  )
  res
  res.map{ r => println(r._1.mkString(" ") +"\t\t->\t"+r._2) }
}

@ beamTest
1 999999999 88888888 7777777 666666 55555 4444 333 22           ->      51.0
1 88888888 999999999 7777777 666666 55555 4444 333 22           ->      51.0
1 999999999 7777777 88888888 666666 55555 4444 333 22           ->      51.0
1 7777777 999999999 88888888 666666 55555 4444 333 22           ->      51.0
1 88888888 7777777 999999999 666666 55555 4444 333 22           ->      51.0
1 7777777 88888888 999999999 666666 55555 4444 333 22           ->      51.0
1 999999999 88888888 666666 7777777 55555 4444 333 22           ->      51.0
1 88888888 999999999 666666 7777777 55555 4444 333 22           ->      51.0