如果您可能丢失重复的密钥:
scala> val map = Map(1->"one", 2->"two", -2->"two")
map: scala.collection.immutable.Map[Int,java.lang.String] = Map((1,one), (2,two), (-2,two))
scala> map.map(_ swap)
res0: scala.collection.immutable.Map[java.lang.String,Int] = Map((one,1), (two,-2))
如果您不想作为多重映射进行访问,而只想作为集合的映射进行访问,那么:
scala> map.groupBy(_._2).mapValues(_.keys.toSet)
res1: scala.collection.immutable.Map[
java.lang.String,scala.collection.immutable.Set[Int]
] = Map((one,Set(1)), (two,Set(2, -2)))
如果您坚持要获得MultiMap
, then:
scala> import scala.collection.mutable.{HashMap, Set, MultiMap}
scala> ( (new HashMap[String,Set[Int]] with MultiMap[String,Int]) ++=
| map.groupBy(_._2).mapValues(Set[Int]() ++= _.keys) )
res2: scala.collection.mutable.HashMap[String,scala.collection.mutable.Set[Int]]
with scala.collection.mutable.MultiMap[String,Int] = Map((one,Set(1)), (two,Set(-2, 2)))