@Override
    public Set<VertexComputeKey> getVertexComputeKeys() {
        return new HashSet<>(Arrays.asList(VertexComputeKey.of(this.property, false), VertexComputeKey.of(VOTE_STRENGTH, true)));
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/computer/clustering/peerpressure/PeerPressureVertexProgram.java