kotlin.collections.groupingBy

inline fun <T, K> Iterable<T>.groupingBy(
    crossinline keySelector: (T) -> K
): Grouping<T, K>

Platform and version requirements: Kotlin 1.1

Creates a Grouping source from a collection to be used later with one of group-and-fold operations using the specified keySelector function to extract a key from each element.

inline fun <T, K> Array<out T>.groupingBy(
    crossinline keySelector: (T) -> K
): Grouping<T, K>

Platform and version requirements: Kotlin 1.1

Creates a Grouping source from an array to be used later with one of group-and-fold operations using the specified keySelector function to extract a key from each element.