@Override
  protected Double computeValue(Double number) {
    return VectorPTFEvaluatorHelper.computeValue(number);
  }
This class evaluates double avg() for a PTF group.

Sum up non-null column values; group result is sum / non-null count.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/ptf/VectorPTFEvaluatorDoubleAvg.java