BUG: RecursionError using `agg` on a resampled SeriesGroupBy

[manoelpqueiroz]

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

---

When you mix resample with groupby and try to use the agg method to supply multiple functions to either a DataFrameGroupBy or SeriesGroupBy, Python suddently exits without even raising an error.

I first thought I was running into this because I was supplying a single column expecting a DataFrame with multiple columns, but I can confirm this happens to me whether I provide a column (variable b) or apply the method to the entire GroupBy (variable c):

Code Sample

import pandas as pd

a = pd.DataFrame({
    'class': {
        0: 'beta', 1: 'alpha', 2: 'alpha', 3: 'gaga', 4: 'beta', 5: 'gaga',
        6: 'beta', 7: 'gaga', 8: 'beta', 9: 'gaga', 10: 'alpha', 11: 'beta',
        12: 'alpha', 13: 'gaga', 14: 'alpha'},
    'value': {
        0: 69, 1: 33, 2: 40, 3: 2, 4: 36, 5: 40, 6: 48, 7: 84, 8: 77, 9: 22,
        10: 55, 11: 82, 12: 37, 13: 88, 14: 41},
    'date': {
        0: pd.Timestamp('2021-02-28 00:00:00'),
        1: pd.Timestamp('2021-11-30 00:00:00'),
        2: pd.Timestamp('2021-02-28 00:00:00'),
        3: pd.Timestamp('2021-04-30 00:00:00'),
        4: pd.Timestamp('2021-02-28 00:00:00'),
        5: pd.Timestamp('2021-04-30 00:00:00'),
        6: pd.Timestamp('2021-07-31 00:00:00'),
        7: pd.Timestamp('2021-01-31 00:00:00'),
        8: pd.Timestamp('2021-01-31 00:00:00'),
        9: pd.Timestamp('2021-01-31 00:00:00'),
        10: pd.Timestamp('2021-04-30 00:00:00'),
        11: pd.Timestamp('2021-10-31 00:00:00'),
        12: pd.Timestamp('2021-09-30 00:00:00'),
        13: pd.Timestamp('2021-04-30 00:00:00'),
        14: pd.Timestamp('2021-05-31 00:00:00')}})

# This will exit Python
b = a\
    .set_index('date')\
    .groupby('class')\
    .resample('M')['value']\
    .agg(['sum', 'size'])

# Not informing a column will ALSO make Python exit
c = a\
    .set_index('date')\
    .groupby('class')\
    .resample('M')\
    .agg(['sum', 'size'])

Problem description

I'm not sure if this method is supported for instances of DatetimeIndexResamplerGroupby objects, but calling it without arguments is valid, giving:

<bound method Resampler.aggregate of <pandas.core.resample.DatetimeIndexResamplerGroupby object at 0x00000163B22B0100>>

Also, while the problem arises with either a Series or a DataFrame, given that using agg with multiple functions on a SeriesGroupBy will correctly create a DataFrame, I would expect the same to happen when resampling with timestamps:

In [1]: a.groupby('class')['value'].agg(['sum', 'size'])
Out[1]:
       sum  size
class
alpha  206     5
beta   312     5
gaga   236     5

Expected Output

                  sum  size
class date
alpha 2021-02-28   40     1
      2021-03-31    0     0
      2021-04-30   55     1
      2021-05-31   41     1
      2021-06-30    0     0
      2021-07-31    0     0
      2021-08-31    0     0
      2021-09-30   37     1
      2021-10-31    0     0
      2021-11-30   33     1
beta  2021-01-31   77     1
      2021-02-28  105     2
      2021-03-31    0     0
      2021-04-30    0     0
      2021-05-31    0     0
      2021-06-30    0     0
      2021-07-31   48     1
      2021-08-31    0     0
      2021-09-30    0     0
      2021-10-31   82     1
gaga  2021-01-31  106     2
      2021-02-28    0     0
      2021-03-31    0     0
      2021-04-30  130     3

Output of pd.show_versions()

INSTALLED VERSIONS

commit : c7f7443
python : 3.9.2.final.0
python-bits : 64
OS : Windows
OS-release : 10
Version : 10.0.18362
machine : AMD64
processor : Intel64 Family 6 Model 142 Stepping 9, GenuineIntel
byteorder : little
LC_ALL : None
LANG : None
LOCALE : pt_BR.cp1252

pandas : 1.3.1
numpy : 1.20.2
pytz : 2021.1
dateutil : 2.8.1
pip : 21.2.1
setuptools : 49.2.1
Cython : None
pytest : None
hypothesis : None
sphinx : 3.5.1
blosc : None
feather : None
xlsxwriter : None
lxml.etree : 4.6.3
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 2.11.3
IPython : 7.24.1
pandas_datareader: None
bs4 : 4.9.3
bottleneck : None
fsspec : None
fastparquet : None
gcsfs : None
matplotlib : 3.4.1
numexpr : None
odfpy : None
openpyxl : 3.0.6
pandas_gbq : None
pyarrow : None
pyxlsb : 1.0.8
s3fs : None
scipy : 1.7.0
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
numba : None

[sebasv]

I just ran your example and got

---------------------------------------------------------------------------
RecursionError                            Traceback (most recent call last)
<ipython-input-1-7682602f0189> in <module>
     27 
     28 # This will exit Python
---> 29 b = a\
     30     .set_index('date')\
     31     .groupby('class')\

~/anaconda3/lib/python3.8/site-packages/pandas/core/resample.py in aggregate(self, func, *args, **kwargs)
    332     def aggregate(self, func, *args, **kwargs):
    333 
--> 334         result = ResamplerWindowApply(self, func, args=args, kwargs=kwargs).agg()
    335         if result is None:
    336             how = func

~/anaconda3/lib/python3.8/site-packages/pandas/core/apply.py in agg(self)
    162         elif is_list_like(arg):
    163             # we require a list, but not a 'str'
--> 164             return self.agg_list_like()
    165 
    166         if callable(arg):

~/anaconda3/lib/python3.8/site-packages/pandas/core/apply.py in agg_list_like(self)
    353                 colg = obj._gotitem(col, ndim=1, subset=selected_obj.iloc[:, index])
    354                 try:
--> 355                     new_res = colg.aggregate(arg)
    356                 except (TypeError, DataError):
    357                     pass

... last 3 frames repeated, from the frame below ...

~/anaconda3/lib/python3.8/site-packages/pandas/core/resample.py in aggregate(self, func, *args, **kwargs)
    332     def aggregate(self, func, *args, **kwargs):
    333 
--> 334         result = ResamplerWindowApply(self, func, args=args, kwargs=kwargs).agg()
    335         if result is None:
    336             how = func

RecursionError: maximum recursion depth exceeded while calling a Python object

the problem doesn't happen when I do

c = a\
    .set_index('date')\
    .groupby('class')\
    .resample('M') \
    .sum()

or

c = a\
    .set_index('date')\
    .groupby('class')\
    .resample('M') \
    .agg('count')

[simonjayhawkins]

On pandas 1.2.5, the first example (b=..) gives the expected output. The second example (c=...) raises RecursionError: maximum recursion depth exceeded in __instancecheck__ which is different from the error on master RecursionError: maximum recursion depth exceeded while calling a Python object

I'll label as a regression for now pending further investigation.

[simonjayhawkins]

first bad commit: [212323f] BUG: DataFrame.agg and apply with 'size' returns a scalar (#39935)

after this commit the error was

2021-08-25T11:17:29.5737203Z Traceback (most recent call last):
2021-08-25T11:17:29.5738655Z   File "../42905.py", line 64, in <module>
2021-08-25T11:17:29.5739824Z     result = grp.resample("M")["value"].agg(["sum", "size"])
2021-08-25T11:17:29.5741294Z   File "/home/runner/work/pandas/pandas/pandas/core/resample.py", line 344, in aggregate
2021-08-25T11:17:29.5742977Z     result = ResamplerWindowApply(self, func, args=args, kwargs=kwargs).agg()
2021-08-25T11:17:29.5744583Z   File "/home/runner/work/pandas/pandas/pandas/core/apply.py", line 196, in agg
2021-08-25T11:17:29.5745877Z     return self.agg_list_like(_axis=_axis)
2021-08-25T11:17:29.5747209Z   File "/home/runner/work/pandas/pandas/pandas/core/apply.py", line 358, in agg_list_like
2021-08-25T11:17:29.5748120Z     new_res = colg.aggregate(a)
2021-08-25T11:17:29.5749318Z   File "/home/runner/work/pandas/pandas/pandas/core/resample.py", line 344, in aggregate
2021-08-25T11:17:29.5750342Z     result = ResamplerWindowApply(self, func, args=args, kwargs=kwargs).agg()
2021-08-25T11:17:29.5751265Z   File "/home/runner/work/pandas/pandas/pandas/core/apply.py", line 188, in agg
2021-08-25T11:17:29.5752011Z     result = self.maybe_apply_str()
2021-08-25T11:17:29.5752754Z   File "/home/runner/work/pandas/pandas/pandas/core/apply.py", line 514, in maybe_apply_str
2021-08-25T11:17:29.5753474Z     value = obj.shape[self.axis]
2021-08-25T11:17:29.5754218Z   File "/home/runner/work/pandas/pandas/pandas/core/resample.py", line 166, in __getattr__
2021-08-25T11:17:29.5755240Z     return object.__getattribute__(self, attr)
2021-08-25T11:17:29.5756835Z AttributeError: 'DatetimeIndexResamplerGroupby' object has no attribute 'shape'

cc @rhshadrach

[rhshadrach]

Thanks @manoelpqueiroz for the report. I'm seeing the same with a git bisect as @simonjayhawkins reported, but don't quite understand it yet. The method BaseGroupBy._selected_obj is being called on master with self._selection as None, resulting in a DataFrame where 1.2.x has it set and returns a Series. It appears to me the current implementation on master would work as expected if this method returned a Series.

I ran a bisect to see where this method started to return a DataFrame with:

a = pd.DataFrame(
    {
        'class': ['beta'],
        'value': [69],
        'date': [pd.Timestamp('2021-02-28 00:00:00')],
    }
)
ndim = a.set_index('date').groupby('class').resample('M')['value']._selected_obj.ndim
assert ndim == 1

and found first bad commit is a222322, cc @jbrockmendel

[jbrockmendel]

This is pretty nasty. Best guess is that in GroupByMixin._gotitem when we do groupby = self._groupby[key] and catch IndexError, we are catching cases that we shouldn't be.