Kotlin
Kotlin
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kotlin.collections.Grouping

Grouping

kotlin-stdlib / kotlin.collections / Grouping 
interface Grouping<T, out K>

Platform and version requirements: Kotlin 1.1

Represents a source of elements with a keyOf function, which can be applied to each element to get its key-

A Grouping structure serves as an intermediate step in group-and-fold operations: they group elements by their keys and then fold each group with some aggregating operation-

It is created by attaching keySelector: (T) -> K function to a source of elements- To get an instance of Grouping use