使用谓词从scala可变映射中删除元素的正确方法是什么 [英] What is the proper way to remove elements from a scala mutable map using a predicate

问题描述

如何在不创建任何新集合的情况下做到这一点?有什么比这更好的吗?

How to do that without creating any new collections? Is there something better than this?

val m = scala.collection.mutable.Map[String, Long]("1" -> 1, "2" -> 2, "3" -> 3, "4" -> 4)
m.foreach(t => if (t._2 % 2 == 0) m.remove(t._1))
println(m)

P.S.在Scala 2.8中

P.S. in Scala 2.8

推荐答案

retain做您想要的.在2.7版中:

retain does what you want. In 2.7:

val a = collection.mutable.Map(1->"one",2->"two",3->"three")
a: scala.collection.mutable.Map[Int,java.lang.String] = 
  Map(2 -> two, 1 -> one, 3 -> three)

scala> a.retain((k,v) => v.length < 4)   

scala> a
res0: scala.collection.mutable.Map[Int,java.lang.String] =
  Map(2 -> two, 1 -> one)

它也可以工作，但我认为它在2.8中仍在不断发展.

It also works, but I think is still in flux, in 2.8.

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