更改元素在列表中的位置

Question

在scala有一个List

var list=List("scala","finagle","anorm","akka","actor","play","jdbc")

如果它包含"akka"类的元素，那么我想将其移至第一位置。

List("akka","scala","finagle","anorm","actor","play","jdbc")

Answer 1

试试这个（注意，我在输入字符串的末尾添加了一个额外的“ akka”副本，以显示它如何收集所有匹配的字符串）：

scala> val inList = List("scala","finagle","anorm","akka","actor","play","akka","jdbc")
inList: List[String] = List(scala, finagle, anorm, akka, actor, play, akka, jdbc)

scala> val partitioned = inList.partition(_ == "akka") // Or whatever partition function suits your need
partitioned: (List[String], List[String]) = (List(akka, akka),List(scala, finagle, anorm, actor, play, jdbc))

scala> val outList = partitioned._1 ::: partitioned._2
outList: List[String] = List(akka, akka, scala, finagle, anorm, actor, play, jdbc)

Answer 2

如果最多只有一个“ akka”：

var (before, after) = list.span(_ != "akka")
//> before  : List[String] = List(scala, finagle, anorm)
//| after  : List[String] = List(akka, actor, play, jdbc)

if (after.isEmpty) list else "akka" :: (before ::: after.tail)
//> res0: List[String] = List(akka, scala, finagle, anorm, actor, play, jdbc)

Answer 3

这是最短的解决方案（尽管在较大的列表中效率不高）：

 var list=List("scala","finagle","anorm","akka","actor","play","jdbc")
 println(list.sortBy(_ != "akka"))  // List(akka, scala, finagle, anorm, actor, play, jdbc)