SeriesGroupby.cumsum raises on object dtype

[agraboso]

import pandas as pd

s = pd.Series(list('ABCDEF'))
grouper = pd.Series([0]*3+[1]*3)

The obvious attempt to obtain

0      A
1     AB
2    ABC
3      D
4     DE
5    DEF
dtype: object

using

s.groupby(grouper).cumsum()

raises a DataError: No numeric types to aggregate. A workaround is available via

s.groupby(grouper).apply(pd.Series.cumsum)

SeriesGroupby.cumsum should follow the behavior of SeriesGroupby.sum, where both s.groupby(grouper).apply(pd.Series.sum) and s.groupby(grouper).sum() produce the correct output:

0    ABC
1    DEF
dtype: object

This was introduced some time between 0.15.2 and 0.18.1, as observed here.

output of pd.show_versions()

INSTALLED VERSIONS
------------------
commit: None
python: 3.5.2.final.0
python-bits: 64
OS: Darwin
OS-release: 15.5.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: en_US.UTF-8
LANG: en_US.UTF-8

pandas: 0.18.1
nose: 1.3.7
pip: 8.1.2
setuptools: 23.0.0
Cython: 0.24
numpy: 1.11.0
scipy: 0.17.1
statsmodels: 0.6.1
xarray: None
IPython: 4.2.0
sphinx: None
patsy: 0.4.1
dateutil: 2.5.3
pytz: 2016.4
blosc: None
bottleneck: None
tables: None
numexpr: 2.6.0
matplotlib: 1.5.1
openpyxl: None
xlrd: 1.0.0
xlwt: None
xlsxwriter: None
lxml: None
bs4: 4.4.1
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: 1.0.13
pymysql: None
psycopg2: None
jinja2: 2.8
boto: None
pandas_datareader: None

[jreback]

I guess, we had some discussion we should actually remove this behavior for .sum. It is pretty confusing as its an implicit (and prob unwanted operation); rather it should be explicit.

see #13416

[rhshadrach]

From #13416 (comment)

Maybe it should be excluded by default even if categorical internal is numeric, and included if numeric_only=True? Thus, groupby agg also should have numeric_only kwd.

groupby(...).sum now has a numeric_only=True argument, so as far as I can tell, the decision was made to have numeric only by default but also support non-numeric. For API consistency, it seems to me that cumsum et al should be the same.

[rhshadrach]

numeric_only=False is now the default consistently, and cumsum on object dtype is #44009. Closing.