@Override
public void combine(Iterable<VertexWithRank> recordsIterable, Collector<VertexWithRank> out) throws Exception {
final Iterator<VertexWithRank> records = recordsIterable.iterator();
VertexWithRank next = records.next();
this.accumulator.setVertexID(next.getVertexID());
double rank = next.getRank();
while (records.hasNext()) {
rank += records.next().getRank();
}