Finding counts of each distinct element in a Scala array?

you can do it like this:

val xs = Array("a", "b", "c", "c", "a", "b", "c", "b", "b", "a")
xs.groupBy(identity).mapValues(_.length)

or like this:

xs.foldLeft(Map[String, Int]().withDefaultValue(0))((acc, x) => acc + (x -> (acc(x) + 1)))

or you could use internal mutability to prevent copying if you want to be more efficient:

def countElems[A](xs: Array[A]): Map[A, Int] = {
  val result = collection.mutable.Map[A, Int]().withDefaultValue(0)
  xs foreach { x => result += (x -> (result(x) + 1)) }
  result.toMap // this copies and makes it immutable, O(number of distinct elements)
}