@Override
    public void combine(final Serializable key, final Iterator<Long> values, final ReduceEmitter<Serializable, Long> emitter) {
        this.reduce(key, values, emitter);
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/computer/clustering/peerpressure/ClusterPopulationMapReduce.java