[Pitch] Sequence grouped(by:) and keyed(by:)

[wowbagger (冀卓疌)]

A relevant post from a few years ago:

Add GroupBy method to Sequence

Introduction Early in my career I worked a lot with C#, and I found the IEnumerable<T> extension methods extremely useful. I think Swift would benefit from adding some equivalents. This pitch is for GroupBy, which would be a method on Sequence that takes a transformation closure to produce a key from each element and returns an array of Group objects that amount to all values that share one value of a key. Motivation Grouping objects by values of some transformation is a common need. Take the…