code: public DataSet<Tuple2<K, LongValue>> getDegrees() {
  		return outDegrees()
  			.union(inDegrees()).name("In- and out-degree")
  			.groupBy(0).sum(1).name("Sum");
  	}
docs: Return the degree of all vertices in the graph.
  
  @return A DataSet of {@code Tuple2<vertexId, degree>}