In [13]: df = pd.DataFrame({"A": pd.to_datetime(['2015', '2017']), "B": [1, 1]}) In [14]: df Out[14]: A B 0 2015-01-01 1 1 2017-01-01 1 In [15]: df.set_index("A").groupby([0, 0]).resample("AS") Out[15]: DatetimeIndexResamplerGroupby [freq=<YearBegin: month=1>, axis=0, closed=left, label=left, convention=e, base=0] In [16]: df.set_index("A").groupby([0, 0]).resample("AS").agg(['sum', 'count']) --------------------------------------------------------------------------- Exception Traceback (most recent call last) <ipython-input-16-5f1c18a8d4ac> in <module>() ----> 1 df.set_index("A").groupby([0, 0]).resample("AS").agg(['sum', 'count']) ~/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/core/resample.py in aggregate(self, arg, *args, **kwargs) 339 340 self._set_binner() --> 341 result, how = self._aggregate(arg, *args, **kwargs) 342 if result is None: 343 result = self._groupby_and_aggregate(arg, ~/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/core/base.py in _aggregate(self, arg, *args, **kwargs) 538 return self._aggregate_multiple_funcs(arg, 539 _level=_level, --> 540 _axis=_axis), None 541 else: 542 result = None ~/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/core/base.py in _aggregate_multiple_funcs(self, arg, _level, _axis) 583 try: 584 colg = self._gotitem(col, ndim=1, subset=obj[col]) --> 585 results.append(colg.aggregate(arg)) 586 keys.append(col) 587 except (TypeError, DataError): ~/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/core/resample.py in aggregate(self, arg, *args, **kwargs) 339 340 self._set_binner() --> 341 result, how = self._aggregate(arg, *args, **kwargs) 342 if result is None: 343 result = self._groupby_and_aggregate(arg, ~/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/core/base.py in _aggregate(self, arg, *args, **kwargs) 538 return self._aggregate_multiple_funcs(arg, 539 _level=_level, --> 540 _axis=_axis), None 541 else: 542 result = None ~/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/core/base.py in _aggregate_multiple_funcs(self, arg, _level, _axis) 582 for col in obj: 583 try: --> 584 colg = self._gotitem(col, ndim=1, subset=obj[col]) 585 results.append(colg.aggregate(arg)) 586 keys.append(col) ~/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/core/base.py in _gotitem(self, key, ndim, subset) 675 for attr in self._attributes]) 676 self = self.__class__(subset, --> 677 groupby=self._groupby[key], 678 parent=self, 679 **kwargs) ~/Envs/pandas-dev/lib/python3.6/site-packages/pandas/pandas/core/base.py in __getitem__(self, key) 241 if self._selection is not None: 242 raise Exception('Column(s) {selection} already selected' --> 243 .format(selection=self._selection)) 244 245 if isinstance(key, (list, tuple, ABCSeries, ABCIndexClass, Exception: Column(s) B already selected