public Object iterate(int currentRow, LeadLagInfo leadLagInfo) throws HiveException {
    Range range = PTFRangeUtil.getRange(winFrame, currentRow, partition, nullsLast);
    PTFPartitionIterator<Object> pItr = range.iterator();
    return calcFunctionValue(pItr, leadLagInfo);
  }
Given the current row, get the aggregation for the window

@throws HiveException
ql/src/java/org/apache/hadoop/hive/ql/udf/ptf/BasePartitionEvaluator.java