BUG: inconsistent behaviour of the method .idxmin between timedelta datatype & int datatypes #48123
Description
Pandas version checks
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I have confirmed this bug exists on the latest version of pandas.
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I have confirmed this bug exists on the main branch of pandas.
Reproducible Example
import pandas as pd
incomplete_df: pd.DataFrame = pd.DataFrame({'event1': [pd.Timedelta("1 days"), pd.Timedelta("2 days"), pd.Timedelta("nat"), pd.Timedelta("5 days") , pd.Timedelta("6 days"), pd.Timedelta("nat"), pd.Timedelta("nat"), pd.Timedelta("11 days"), pd.Timedelta("nat"), pd.Timedelta("15 days")],
'event2': [pd.Timedelta("nat"), pd.Timedelta("1 days") , pd.Timedelta("nat"), pd.Timedelta("3 days") , pd.Timedelta("4 days"), pd.Timedelta("7 days") , pd.Timedelta("nat"), pd.Timedelta("12 days"), pd.Timedelta("nat"), pd.Timedelta("17 days")],
'event3': [pd.Timedelta("nat"), pd.Timedelta("nat"), pd.Timedelta("nat"), pd.Timedelta("nat"), pd.Timedelta("6 days"), pd.Timedelta("4 days") , pd.Timedelta("9 days") , pd.Timedelta("nat"), pd.Timedelta("3 days") , pd.Timedelta("nat")]})
incomplete_df['reason'] = "Reason is " + incomplete_df.idxmin(axis="columns")Issue Description
The above code will throw:
ValueError: attempt to get argmin of an empty sequence
However, using this code:
import pandas as pd
import numpy as np
incomplete_df = pd.DataFrame({'event1': [1, 2 ,np.nan,5 ,6,np.nan,np.nan,11 ,np.nan,15],
'event2': [np.nan,1 ,np.nan,3 ,4,7 ,np.nan,12 ,np.nan,17],
'event3': [np.nan,np.nan,np.nan,np.nan,6,4 ,9 ,np.nan,3 ,np.nan]})
incomplete_df['reason'] = "Reason is " + incomplete_df.idxmin(axis="columns")returns a dataframe (incomplete_df) with a fourth column with None when the three columns are np.nan
Expected Behavior
The documentation states:
Raises ValueError If the row/column is empty.
This is currently wrong when it comes to integers.
Expected behaviour:
some consistency between the two datatypes.
With those two stackoverflow posts in mind (https://stackoverflow.com/questions/21188151/pandas-getting-the-name-of-the-minimum-column/73346957#73346957, and https://stackoverflow.com/questions/73354436/pandas-getting-the-name-of-the-minimum-column-with-timedelta-datatype), it is quite obvious, the expected behaviour should not be Raises ValueError If the row/column is empty but rather sets None in the created row/column when the row/column is empty. Or an optional argument should be added to determine what behaviour is desired by the user.
Installed Versions
INSTALLED VERSIONS
commit : e8093ba
python : 3.10.2.final.0
python-bits : 64
OS : Windows
OS-release : 10
Version : 10.0.22000
machine : AMD64
processor : AMD64 Family 25 Model 80 Stepping 0, AuthenticAMD
byteorder : little
LC_ALL : None
LANG : None
LOCALE : English_United Kingdom.1252
pandas : 1.4.3
numpy : 1.22.0
pytz : 2021.3
dateutil : 2.8.2
setuptools : 58.1.0
pip : 22.2.2
Cython : None
pytest : 7.1.2
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.0.3
IPython : 8.0.0
pandas_datareader: None
bs4 : 4.11.1
bottleneck : None
brotli : None
fastparquet : None
fsspec : 2022.5.0
gcsfs : None
markupsafe : 2.0.1
matplotlib : 3.5.2
numba : 0.55.2
numexpr : None
odfpy : None
openpyxl : 3.0.9
pandas_gbq : None
pyarrow : None
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : 1.7.3
snappy : None
sqlalchemy : 1.4.36
tables : None
tabulate : None
xarray : None
xlrd : 2.0.1
xlwt : None
zstandard : None