BUG: DataFrame.groupby() interprets tuple as list of keys by GuessWhoSamFoo · Pull Request #17996 · pandas-dev/pandas (original) (raw)

In [2]: df = pd.DataFrame([[1, 2, 3, 4], [3, 4, 5, 6], [1, 4, 2, 3]],
   ...:                            columns=pd.MultiIndex.from_arrays([['a', 'b', 'b', 'c'],
   ...:                                                               [1, 1, 2, 2]]))

In [3]: df.groupby([('b', 1)]).groups
Out[3]: {2: Int64Index([0], dtype='int64'), 4: Int64Index([1, 2], dtype='int64')}

In [4]: df.groupby(('b', 1)).groups
Out[4]: {2: Int64Index([0], dtype='int64'), 4: Int64Index([1, 2], dtype='int64')}