@Override
      public Iterator<Object> iterator() {
        return new Iterator<Object> () {
          long value = 0;

          @Override
          public boolean hasNext() {
            return true;
          }

          @Override
          public Object next() {
            return ++value;
          }

          @Override
          public void remove() {
          }
        };
      }
Unit test for the vectorized GROUP BY operator.
ql/src/test/org/apache/hadoop/hive/ql/exec/vector/TestVectorGroupByOperator.java