twitter/scalding — pull request #36 by johnynek (2012-03-23 16:00:05+00:00)
Title: Some cleanups of reduce and Operations

* made reduce just a call to mapReduceMap. It's underlying Operation already was, this makes the scala code clearer and removes code.

* removed some allocations of Some in MRMBy. Dropping into "java-like" code for the internals where it could reduce memory usage, may be worth it.

* changed the order of toList concatenation. This changes the memory allocation/time complexity from O(N^2) to O(N). This could eliminate some of the OOM issues that have been reported with toList.