Question

我见过很多关于Scala集合的问题但无法决定。到目前为止，此question是最有用的。

我认为问题的核心是双重的： 1）这个用例的最佳集合是什么？ 2）推荐使用哪种方法？

详细说明：

我正在实现一种迭代集合中所有元素的算法搜索符合特定标准的那个。搜索之后，下一步是再次使用新标准进行搜索，但在可能性中没有选择的元素。我们的想法是创建一个序列，其中包含按标准排序的所有原始元素（在每个新选择时都会更改）。原始序列并不需要进行排序，但可能存在重复（算法一次只能选择一个）。一小部分Ints的例子（只是为了简化）：

object Foo extends App {
  def f(already_selected: Seq[Int])(element: Int): Double =
  // something more complex happens here,
  // specially something take takes 'already_selected' into account
  math.sqrt(element)

  //call to the algorithm

  val (result, ti) = Tempo.time(recur(Seq.fill(9900)(Random.nextInt), Seq()))
  println("ti = " + ti)

  //algorithm
  def recur(collection: Seq[Int], already_selected: Seq[Int]): (Seq[Int], Seq[Int]) =
     if (collection.isEmpty) (Seq(), already_selected)
     else {
        val selected = collection maxBy f(already_selected)
        val rest = collection diff Seq(selected) //this part doesn't seem to be efficient
        recur(rest, selected +: already_selected)
     }
}

object Tempo {
 def time[T](f: => T): (T, Double) = {
    val s = System.currentTimeMillis
    (f, (System.currentTimeMillis - s) / 1000d)
 }
}

Answer 1

尝试@inline和icn建议How can I idiomatically "remove" a single element from a list in Scala and close the gap?：

object Foo extends App {
  @inline
  def f(already_selected: Seq[Int])(element: Int): Double =
  // something more complex happens here,
  // specially something take takes 'already_selected' into account
    math.sqrt(element)

  //call to the algorithm

  val (result, ti) = Tempo.time(recur(Seq.fill(9900)(Random.nextInt()).zipWithIndex, Seq()))
  println("ti = " + ti)

  //algorithm
  @tailrec
  def recur(collection: Seq[(Int, Int)], already_selected: Seq[Int]): Seq[Int] =
    if (collection.isEmpty) already_selected
    else {
      val (selected, i) = collection.maxBy(x => f(already_selected)(x._2))
      val rest = collection.patch(i, Nil, 1) //this part doesn't seem to be efficient
      recur(rest, selected +: already_selected)
    }
}

object Tempo {
  def time[T](f: => T): (T, Double) = {
    val s = System.currentTimeMillis
    (f, (System.currentTimeMillis - s) / 1000d)
  }
}

对集合进行增量（多次传递）过滤的理想集合是什么？

1 个答案: