E.g. for List(1, 1, 1, 2, 3, 3, 4)
it would be Set(1, 3)
, because 1 and 3 are the only elements which occur multiple times.
val s = List(1, 1, 1, 2, 3, 3, 4) // a list with non-unique elements
(s diff s.distinct) toSet // Set(1, 3)
A bit more convoluted but you can avoid having to call toSet.toList
, first group the integers:
scala> s.groupBy(identity)
res13: scala.collection.immutable.Map[Int,List[Int]] =
Map(2 -> List(2), 4 -> List(4), 1 -> List(1, 1, 1), 3 -> List(3, 3))
Then collect only the one were the list has length greater as 1:
scala> s.groupBy(identity).collect { case (v, l) if l.length > 1 => v }
res17: scala.collection.immutable.Iterable[Int] = List(1, 3)
If you want a Set
just call toSet
.