Scala Cookbook

11.18. Getting the Keys or Values from a Map

Problem

You want to get all of the keys or values from a map.

Solution

To get the keys, use keySet to get the keys as a Set, keys to get an Iterable, or keysIterator to get the keys as an iterator:

scala> val states = Map("AK" -> "Alaska", "AL" -> "Alabama", "AR" -> "Arkansas")
states: scala.collection.immutable.Map[String,String] =
  Map(AK -> Alaska, AL -> Alabama, AR -> Arkansas)

scala> states.keySet
res0: scala.collection.immutable.Set[String] = Set(AK, AL, AR)

scala> states.keys
res1: Iterable[String] = Set(AK, AL, AR)

scala> states.keysIterator
res2: Iterator[String] = non-empty iterator

To get the values from a map, use the values method to get the values as an Iterable, or valuesIterator to get them as an Iterator:

scala> states.values
res0: Iterable[String] = MapLike(Alaska, Alabama, Arkansas)

scala> states.valuesIterator
res1: Iterator[String] = non-empty iterator

As shown in these examples, keysIterator and valuesIterator return an iterator from the map data. I tend to prefer these methods because they don’t create a new collection; they just provide an iterator to walk over the existing elements.