@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