twitter/scalding — pull request #197 by johnynek (2012-10-02 08:30:13+00:00)
Title: Rewrite of CoGrouping2 in Typed-API, allows custom joiners

This fixes the efficiency issue with doing operations on Grouped[K,V] before a join.

It also adds a syntax for custom cogrouping (see Grouped.cogroup)

Finally it implements all typed joins in terms of the above (which turned out to require splunking through several weird and underdocumented cascading issues).