In [19]: import pandas as pd In [20]: df = pd.DataFrame({'A': [0, 0, 0, 1, 1, 1], ...: 'B': [1, 1, 2, 2, 3, 3], ...: 'C': [1, 2, 3, 4, 5, 6]}) In [26]: df.groupby(pd.Grouper(key='A')).count() Out[26]: B C A 0 3 3 1 3 3

In [27]: df.groupby([pd.Grouper(key='A')]).count() --------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-27-f4f86763ebfc> in <module>() ----> 1 df.groupby([pd.Grouper(key='A')]).count() /Users/measejm1/anaconda/lib/python3.5/site-packages/pandas/core/generic.py in groupby(self, by, axis, level, as_index, sort, group_keys, squeeze, **kwargs) 3776 return groupby(self, by=by, axis=axis, level=level, as_index=as_index, 3777 sort=sort, group_keys=group_keys, squeeze=squeeze, -> 3778 **kwargs) 3779 3780 def asfreq(self, freq, method=None, how=None, normalize=False): /Users/measejm1/anaconda/lib/python3.5/site-packages/pandas/core/groupby.py in groupby(obj, by, **kwds) 1425 raise TypeError('invalid type: %s' % type(obj)) 1426 -> 1427 return klass(obj, by, **kwds) 1428 1429 /Users/measejm1/anaconda/lib/python3.5/site-packages/pandas/core/groupby.py in __init__(self, obj, keys, axis, level, grouper, exclusions, selection, as_index, sort, group_keys, squeeze, **kwargs) 352 level=level, 353 sort=sort, --> 354 mutated=self.mutated) 355 356 self.obj = obj /Users/measejm1/anaconda/lib/python3.5/site-packages/pandas/core/groupby.py in _get_grouper(obj, key, axis, level, sort, mutated) 2400 sort=sort, 2401 in_axis=in_axis) \ -> 2402 if not isinstance(gpr, Grouping) else gpr 2403 2404 groupings.append(ping) /Users/measejm1/anaconda/lib/python3.5/site-packages/pandas/core/groupby.py in __init__(self, index, grouper, obj, name, level, sort, in_axis) 2197 2198 # get the new grouper -> 2199 grouper = self.grouper._get_binner_for_grouping(self.obj) 2200 self.obj = self.grouper.obj 2201 self.grouper = grouper /Users/measejm1/anaconda/lib/python3.5/site-packages/pandas/core/groupby.py in _get_binner_for_grouping(self, obj) 290 group_axis = obj._get_axis(self.axis) 291 return Grouping(group_axis, None, obj=obj, name=self.key, --> 292 level=self.level, sort=self.sort, in_axis=False) 293 294 @property /Users/measejm1/anaconda/lib/python3.5/site-packages/pandas/core/groupby.py in __init__(self, index, grouper, obj, name, level, sort, in_axis) 2213 t = self.name or str(type(self.grouper)) 2214 raise ValueError("Grouper for '%s' not 1-dimensional" % t) -> 2215 self.grouper = self.index.map(self.grouper) 2216 if not (hasattr(self.grouper, "__len__") and 2217 len(self.grouper) == len(self.index)): /Users/measejm1/anaconda/lib/python3.5/site-packages/pandas/indexes/base.py in map(self, mapper) 2238 applied : array 2239 """ -> 2240 return self._arrmap(self.values, mapper) 2241 2242 def isin(self, values, level=None): pandas/src/generated.pyx in pandas.algos.arrmap_int64 (pandas/algos.c:94003)() TypeError: 'NoneType' object is not callable

In [27]: df.groupby([pd.Grouper(key='A')]).count() Out[27]: B C A 0 3 3 1 3 3