facebook/immutable-js — pull request #211 by abergs (2014-11-21 14:36:40+00:00)
Title: [Suggestion] for ordered groupBy

I am grouping a sorted list, and want the map created by groupBy to reflect the order in the list.
Locally i just switched the map to a OrderedMap and the behavior was working as expected.

I am typing this out directly in GitHub so it might contains bugs. My local modifications were naive and always did OrderedMap, which might not be as lean/performant as you want.

Any thoughts?