BUG: apply behaviour changed when using function that returns tuple

[martijnvanattekum]

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

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

• (optional) I have confirmed this bug exists on the master branch of pandas.

---

Code Sample, a copy-pastable example

import seaborn as sns
import pandas as pd
import numpy as np

def get_mean_sd(column):
    return np.mean(column), np.std(column)

iris = sns.load_dataset("iris")[["sepal_length", "sepal_width", "petal_length", "petal_width"]]
iris.apply(get_mean_sd)

Problem description

In version 1.0, the result was a pandas series of tuples, whereas in 1.1 the result is a data frame, thus breaking existing code that depends on apply.

The result from 1.1 is

   sepal_length  sepal_width  petal_length  petal_width
0      5.843333     3.057333      3.758000     1.199333
1      0.825301     0.434411      1.759404     0.759693

Expected Output

The output from version 1.0 was:

sepal_length     (5.843333333333334, 0.8253012917851409)
sepal_width     (3.0573333333333337, 0.4344109677354946)
petal_length     (3.7580000000000005, 1.759404065775303)
petal_width     (1.1993333333333336, 0.7596926279021594)
dtype: object

Output of pd.show_versions()

For 1.0.3:
INSTALLED VERSIONS

commit : None
python : 3.8.2.final.0
python-bits : 64
OS : Linux
OS-release : 3.10.0-1127.18.2.el7.x86_64
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : en_US.utf-8
LANG : en_US.utf-8
LOCALE : en_US.UTF-8

pandas : 1.0.3
numpy : 1.18.1
pytz : 2020.1
dateutil : 2.8.1
pip : 20.0.2
setuptools : 46.4.0.post20200518
Cython : None
pytest : None
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : None
IPython : 7.13.0
pandas_datareader: None
bs4 : None
bottleneck : None
fastparquet : None
gcsfs : None
lxml.etree : None
matplotlib : 3.2.1
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : None
pytables : None
pytest : None
pyxlsb : None
s3fs : None
scipy : 1.4.1
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
xlsxwriter : None
numba : None

For 1.1.1:
INSTALLED VERSIONS

commit : f2ca0a2
python : 3.8.2.final.0
python-bits : 64
OS : Linux
OS-release : 3.10.0-1127.18.2.el7.x86_64
Version : #1 SMP Sun Jul 26 15:27:06 UTC 2020
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : en_US.utf-8
LANG : en_US.utf-8
LOCALE : en_US.UTF-8

pandas : 1.1.1
numpy : 1.18.1
pytz : 2020.1
dateutil : 2.8.1
pip : 20.0.2
setuptools : 46.4.0.post20200518
Cython : None
pytest : None
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : None
IPython : 7.13.0
pandas_datareader: None
bs4 : None
bottleneck : None
fsspec : None
fastparquet : None
gcsfs : None
matplotlib : 3.2.1
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : None
pytables : None
pyxlsb : None
s3fs : None
scipy : 1.4.1
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
numba : None

[jbrockmendel]

This looks like a duplicate of #35518. @martijnvanattekum is that correct?

[martijnvanattekum]

Yes, you are correct. I somehow did not find that report.

…

On Tue, Sep 1, 2020 at 6:42 PM jbrockmendel ***@***.***> wrote: This looks like a duplicate of #35518 <#35518>. @martijnvanattekum <https://github.com/martijnvanattekum> is that correct? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#36042 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AETQM7KZ23RMQJEHBRFUYG3SDUP6HANCNFSM4QR26DYA> .

[simonjayhawkins]

closing as duplicate