BUG: DataFrame.explode is failing on scalar int value.

[galipremsagar]

• 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.

---

Note: Please read this guide detailing how to provide the necessary information for us to reproduce your bug.

Code Sample, a copy-pastable example

>>> import pandas as pd
>>> import numpy as np
>>> df = pd.DataFrame({0: [[0, 1, 2], 'foo', [], [3, 4]],
...                    1: 1,
...                    2: [['a', 'b', 'c'], np.nan, [], ['d', 'e']]})
>>> df
           0  1          2
0  [0, 1, 2]  1  [a, b, c]
1        foo  1        NaN
2         []  1         []
3     [3, 4]  1     [d, e]
>>> df.columns
Int64Index([0, 1, 2], dtype='int64')
>>> df.explode(0)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/pgali/anaconda3/envs/cudf_dev/lib/python3.8/site-packages/pandas/core/frame.py", line 8229, in explode
    assert isinstance(column, (str, tuple))
AssertionError
>>> df.explode([0])
     0  1          2
0    0  1  [a, b, c]
0    1  1  [a, b, c]
0    2  1  [a, b, c]
1  foo  1        NaN
2  NaN  1         []
3    3  1     [d, e]
3    4  1     [d, e]
>>> 

Problem description

Looks like passing a scalar int to column is causing a failure in DataFrame.explode, but passing a list of int's is working.

Expected Output

>>> df.explode(0)
     0  1          2
0    0  1  [a, b, c]
0    1  1  [a, b, c]
0    2  1  [a, b, c]
1  foo  1        NaN
2  NaN  1         []
3    3  1     [d, e]
3    4  1     [d, e]

Output of pd.show_versions()

INSTALLED VERSIONS

commit : 5f648bf
python : 3.8.10.final.0
python-bits : 64
OS : Linux
OS-release : 5.11.0-27-generic
Version : #29~20.04.1-Ubuntu SMP Wed Aug 11 15:58:17 UTC 2021
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 1.3.2
numpy : 1.21.2
pytz : 2021.1
dateutil : 2.8.2
pip : 21.2.4
setuptools : 57.4.0
Cython : 0.29.24
pytest : 6.2.4
hypothesis : 6.17.2
sphinx : 4.1.2
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.0.1
IPython : 7.27.0
pandas_datareader: None
bs4 : 4.9.3
bottleneck : None
fsspec : 2021.07.0
fastparquet : None
gcsfs : None
matplotlib : None
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : 5.0.0
pyxlsb : None
s3fs : None
scipy : None
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
numba : 0.53.1

[simonjayhawkins]

Thanks @galipremsagar for the report.

Looks like passing a scalar int to column is causing a failure in DataFrame.explode, but passing a list of int's is working.

1.2.5 was giving the expected output.

[simonjayhawkins]

first bad commit: [41a94b0] EHN: multi-column explode (#39240) (#40770)