Yes, different. `BinGrouper.indices` must be a dict which key is timestamp. The logic cannot be replaced with `_groupby_indices`.
```
>>> b.indices
defaultdict(<type 'list'>, {Timestamp('2013-12-31 00:00:00', offset='M'): [6, 7], Timestamp('2013-10-31 00:00:00', offset='M'): [2, 3, 4, 5], Timestamp('2013-01-31 00:00:00', offset='M'): [0, 1]})
```