What is the proper way to remove elements from a scala mutable map using a predicate

Question

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\"         


        

Answer 1

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)

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