cast to float when using groupby.agg with function returning int on float input · Issue #17035 · pandas-dev/pandas (original) (raw)

Code Sample, a copy-pastable example if possible

In [2]: df = pd.DataFrame([[1], [2], [3.3]])

In [3]: df.groupby([1,1,1]).agg(len) Out[3]: 0 1 3.0

Problem description

The result of len should be int, regardless of the input. This is not specific to len: lambda x : 3 results in the same.

Expected Output

Compare to

In [4]: df.apply(len) Out[4]: 0 3 dtype: int64

In [5]: df.groupby([1,1,1]).apply(len) Out[5]: 1 3 dtype: int64

In [6]: df.astype(int).groupby([1,1,1]).agg(len) Out[6]: 0 1 3

Output of pd.show_versions()

INSTALLED VERSIONS ------------------ commit: 9e7666dpython: 3.5.3.final.0 python-bits: 64 OS: Linux OS-release: 4.9.0-3-amd64 machine: x86_64 processor: byteorder: little LC_ALL: None LANG: it_IT.UTF-8 LOCALE: it_IT.UTF-8

pandas: 0.21.0.dev+265.g9e7666dae
pytest: 3.0.6
pip: 9.0.1
setuptools: None
Cython: 0.25.2
numpy: 1.12.1
scipy: 0.19.0
xarray: None
IPython: 5.1.0.dev
sphinx: 1.5.6
patsy: 0.4.1
dateutil: 2.6.0
pytz: 2017.2
blosc: None
bottleneck: 1.2.1
tables: 3.3.0
numexpr: 2.6.1
feather: 0.3.1
matplotlib: 2.0.2
openpyxl: None
xlrd: 1.0.0
xlwt: 1.1.2
xlsxwriter: 0.9.6
lxml: None
bs4: 4.5.3
html5lib: 0.999999999
sqlalchemy: 1.0.15
pymysql: None
psycopg2: None
jinja2: 2.9.6
s3fs: None
pandas_gbq: None
pandas_datareader: 0.2.1