Thanks, but failed in test. I think simply passing `bins` to existing method shouldn't work, because `bins` are corresponding to frequencies to be split, not index. Thus its length can differ from index.

Using dataframe in above example, returnes values are different from expected.
```
>>> list(pd.core.groupby._groupby_indices(grouped.grouper.bins).iteritems())
[(8, array([11])), (2, array([0, 1, 2, 3, 4, 5, 6, 7, 8])), (6, array([ 9, 10]))]
````
```