public Object getPartitionAgg() throws HiveException {
    return calcFunctionValue(partition.iterator(), null);
  }
Get the aggregation for the whole partition. Used in the case where windowing
is unbounded or the function value is calculated based on all the rows in the
partition such as percent_rank().
@return the aggregated result
@throws HiveException
ql/src/java/org/apache/hadoop/hive/ql/udf/ptf/BasePartitionEvaluator.java