@Override
  public Object getGroupResult() {
    return denseRank;
  }
This class evaluates rank() for a PTF group.

Dense rank starts at 1; the same dense rank is streamed to the output column as repeated; after
the last group row, the dense rank incremented by 1.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/ptf/VectorPTFEvaluatorDenseRank.java