查找Scala數組中每個不同元素的計數？

Question

查找Scala數組中每個不同元素的計數的最有效實現是什麼？

Answer 1

，你可以做這樣的：

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

或像這樣：

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

，或者您可以使用內置的可變性，以防止複製，如果你想成爲更高效：

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) 
}