BUG: SeriesGroupBy.value_counts() throws IndexError if there is only one group · Issue #42618 · pandas-dev/pandas (original) (raw)

Code Sample, a copy-pastable example

import pandas as pd pd.DataFrame([[0, 1]], columns=('a', 'b')).groupby('a')['b'].value_counts()

IndexError Traceback (most recent call last) in ----> 1 pd.DataFrame([[0,1]], columns=('a', 'b')).groupby('a')['b'].value_counts()

~/.venvs/python3/lib/python3.9/site-packages/pandas/core/groupby/generic.py in value_counts(self, normalize, sort, ascending, bins, dropna) 762 if not len(lchanges): 763 inc = lchanges --> 764 inc[idx] = True # group boundaries are also new values 765 out = np.diff(np.nonzero(np.r_[inc, True])[0]) # value counts 766

IndexError: index 0 is out of bounds for axis 0 with size 0

Problem description

Calling value_counts() on a SeriesGroupBy throws an IndexError when there is only one group.

Expected Output

a b 0 1 1 Name: b, dtype: int64

Output of pd.show_versions()

INSTALLED VERSIONS

commit : f00ed8f
python : 3.9.4.final.0
python-bits : 64
OS : Darwin
OS-release : 19.6.0
Version : Darwin Kernel Version 19.6.0: Mon Apr 12 20:57:45 PDT 2021; root:xnu-6153.141.28.1~1/RELEASE_X86_64
machine : x86_64
processor : i386
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 1.3.0
numpy : 1.20.2
pytz : 2021.1
dateutil : 2.8.1
pip : 21.0.1
setuptools : 54.2.0
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 : 7.23.0
pandas_datareader: None
bs4 : None
bottleneck : None
fsspec : None
fastparquet : None
gcsfs : None
matplotlib : None
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : 4.0.0
pyxlsb : None
s3fs : None
scipy : None
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
numba : None