@VisibleForTesting
  void preFinishPartition() throws HiveException {
    int rows = size();

    positionCache = new RowPositionInBatch[rows + 1];
    partitionResults = new PartitionResults(rows);
    jumpToFirstBlock();
  }
Returns the values of ordering columns from a given batch and given row in an Object[].
@param vectorizedRowBatch
@param rowIndexInBatch
@return
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/ptf/VectorPTFGroupBatches.java