public static Set<String> vertexComputeKeysAsSet(final Set<VertexComputeKey> vertexComputeKeySet) {
        final Set<String> set = new HashSet<>(vertexComputeKeySet.size());
        for (final VertexComputeKey key : vertexComputeKeySet) {
            set.add(key.getKey());
        }
        return set;
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/computer/util/VertexProgramHelper.java