private static Pair<GroupByDesc,VectorGroupByDesc> buildGroupByDescType(
      VectorizationContext ctx,
      String aggregate,
      GenericUDAFEvaluator.Mode mode,
      String column,
      TypeInfo dataType) {

    AggregationDesc agg = buildAggregationDesc(ctx, aggregate, mode,
        column, dataType);
    ArrayList<AggregationDesc> aggs = new ArrayList<AggregationDesc>();
    aggs.add(agg);

    ArrayList<String> outputColumnNames = new ArrayList<String>();
    outputColumnNames.add("_col0");

    GroupByDesc desc = new GroupByDesc();
    VectorGroupByDesc vectorDesc = new VectorGroupByDesc();

    desc.setOutputColumnNames(outputColumnNames);
    desc.setAggregators(aggs);
    vectorDesc.setProcessingMode(ProcessingMode.GLOBAL);

    return new Pair<GroupByDesc,VectorGroupByDesc>(desc, vectorDesc);
  }
Unit test for the vectorized GROUP BY operator.
ql/src/test/org/apache/hadoop/hive/ql/exec/vector/TestVectorGroupByOperator.java