stratosphere/stratosphere — pull request #269 by StephanEwen (2013-11-11 23:07:16+00:00)
Title: Added count() function on grouped data

Added a function count() to count elements in a group and return a two tuple with original group value and count.

Allows to write code like:
```
val words = input flatMap { _.toLowerCase().split("""\W+""") filter { _ != "" } }
val counts = words groupBy { x => x } count()
```