API: quantile function over columns transposes dataframe

[tomvansteijn]

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

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

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Code snippet

import pandas as pd
import numpy as np

df = pd.DataFrame(data={'a': np.arange(100), 'b': np.arange(100),})

df = df.quantile([0.2, 0.5, 0.8], axis=1)

Problem description

Using DataFrame.quantile over axis=1 with multiple values for q transposes the dataframe. I would expect the quantiles to appear over the specified axis, so along the columns axis when axis = 1, and along rows when axis = 0. Ofcourse, an easy fix is a call to DataFrame.transpose. Ideally this should not be necessary in my opinion.

Expected Output

Quantile values over the specified axis without transposing the dataframe.

Output of pd.show_versions()

C:\Anaconda64\lib\site-packages\setuptools\distutils_patch.py:26: UserWarning: Distutils was imported before Setuptools. This usage is discouraged and may exhibit undesirable behaviors or errors. Please use Setuptools' objects directly or at least import Setuptools first.
"Distutils was imported before Setuptools. This usage is discouraged "

INSTALLED VERSIONS

commit : None
python : 3.7.6.final.0
python-bits : 64
OS : Windows
OS-release : 10
machine : AMD64
processor : Intel64 Family 6 Model 158 Stepping 10, GenuineIntel
byteorder : little
LC_ALL : None
LANG : nl_NL.UTF-8
LOCALE : None.None

pandas : 1.0.5
numpy : 1.18.5
pytz : 2020.1
dateutil : 2.8.1
pip : 20.1.1
setuptools : 49.2.0.post20200712
Cython : 0.29.21
pytest : 5.4.3
hypothesis : 5.19.3
sphinx : 3.1.2
blosc : None
feather : None
xlsxwriter : 1.2.9
lxml.etree : 4.5.2
html5lib : 1.1
pymysql : None
psycopg2 : None
jinja2 : 2.11.2
IPython : 7.16.1
pandas_datareader: None
bs4 : 4.9.1
bottleneck : 1.3.2
fastparquet : None
gcsfs : None
lxml.etree : 4.5.2
matplotlib : 3.2.2
numexpr : 2.7.1
odfpy : None
openpyxl : 3.0.4
pyarrow : None
pytables : None
pytest : 5.4.3
pyxlsb : None
s3fs : None
scipy : 1.3.1
sqlalchemy : 1.3.18
tables : 3.6.1
tabulate : None
xarray : None
xlrd : 1.2.0
xlwt : 1.3.0
xlsxwriter : 1.2.9
numba : 0.50.1

[simonjayhawkins]

Thanks @tomvansteijn for the report.

This is not a bug. This is the expected behaviour so closing. lmk if I misunderstood something and i'll reopen.

from https://pandas.pydata.org/pandas-docs/dev/reference/api/pandas.DataFrame.quantile.html

Returns
Series or DataFrame
If q is an array, a DataFrame will be returned where the
index is q, the columns are the columns of self, and the values are the quantiles.

[tomvansteijn]

Thanks @simonjayhawkins for the clarification. You are right this is not a bug. In usage I think it would make more sense when the columns are q and the index is preserved when computing quantiles over the columns. Currently a transpose is needed to undo the implicit transpose in DataFrame.quantile.

Is it worthwile to label this an enhancement and reopen?

[simonjayhawkins]

Is it worthwile to label this an enhancement and reopen?

sure