apache/spark — pull request #2679 by ankurdave (2014-10-06 16:39:44+00:00)
Title: [SPARK-3818] Graph coarsening

Listing 7 in the [GraphX OSDI paper](http://ankurdave.com/dl/graphx-osdi14.pdf) contains pseudocode for a coarsening operator that allows merging edges that satisfy an edge predicate, collapsing vertices connected by merged edges. This PR provides an implementation of this operator.