@Override
      public boolean equals(Object o) {
        if (this == o) {
          return true;
        }
        if (o == null || getClass() != o.getClass()) {
          return false;
        }
        RowData rowData = (RowData) o;
        return Objects.equals(columnValues, rowData.columnValues);
      }
Evaluator for calculating the dense rank.
SELECT dense_rank(expression1[, expressionn]*) WITHIN GROUP (ORDER BY col1[, coln]*)
Implementation is based on hypothetical rank calculation but the group of values are considered distinct.
Since the source of the input stream is not sorted a HashSet is used for filter out duplicate values
which can lead to OOM in large data sets.
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDAFDenseRank.java