twitter/scalding — pull request #724 by johnynek (2013-12-16 19:32:43+00:00)
Title: Don't convert back to TypedPipe from KeyedList until needed

This does not automatically go back to TypedPipe after a reduce, so you can first reduce, then join. Makes making efficient joins easier to write.

The next thing I want is to be able to join joined things (so, .join(CoGrouped)). I think I know how to do this. That should pretty much fix up the ability to join + reduce arbitrarily in one MR pass.