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BUG: Pandas squashes 1-dimensional Numpy array with shape (1,) down to a 0-dimensional array #59249

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sunghjung3 opened this issue Jul 15, 2024 · 2 comments
Open
3 tasks done

BUG: Pandas squashes 1-dimensional Numpy array with shape (1,) down to a 0-dimensional array #59249

sunghjung3 opened this issue Jul 15, 2024 · 2 comments
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@Animesh-Shukla
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Bug Needs Triage Issue that has not been reviewed by a pandas team member

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@sunghjung3
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sunghjung3 commented Jul 15, 2024 •
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Pandas version checks

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Reproducible Example

import pandas as pd
import numpy as np

df = pd.DataFrame(columns=['x'])
arr0 = np.array([1., 2.])
df.loc[0, "x"] = arr0
print(df.loc[0, "x"].shape)  # prints (2,)
arr1 = np.array([1.])
df.loc[1, "x"] = arr1
print(df.loc[1, "x"].shape)  # prints (). Should print (1,)

Issue Description

When a 1-dimensional Numpy array that only has 1 entry is stored to a DataFrame, Pandas seems to automatically make it a 0-dimensional array.

This is extremely inconvenient when the entries of both df.loc[0, "x"] and df.loc[1, "x"] are accessed later like df.loc[1, "x"][i] just for it to cause Numpy to raise an IndexError because df.loc[1, "x"] is now a 0-dimensional array, not a 1-dimensional array.

NOTE: This was not an issue in Pandas 2.0.0, but it is in version 2.2.2. I am not sure exactly which version in between this was introduced.

FYI: If a higher dimensional array with 1 entry is stored (e.g. np.array([[1.]])), then the shape is correctly preserved. It is only an issue when the array is 1-dimensional.

Expected Behavior

print(df.loc[1, "x"].shape) should print (1,).

Installed Versions

INSTALLED VERSIONS

commit : d9cdd2e
python : 3.11.9.final.0
python-bits : 64
OS : Linux
OS-release : 4.18.0-477.15.1.el8_8.x86_64
Version : #1 SMP Wed Jun 28 15:04:18 UTC 2023
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 2.2.2
numpy : 1.26.4
pytz : 2024.1
dateutil : 2.9.0
setuptools : 70.3.0
pip : 24.0
Cython : None
pytest : 8.2.2
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.1.4
IPython : 8.26.0
pandas_datareader : None
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : None
bottleneck : None
dataframe-api-compat : None
fastparquet : None
fsspec : 2024.6.1
gcsfs : None
matplotlib : 3.9.1
numba : 0.60.0
numexpr : 2.10.0
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : None
pyreadstat : None
python-calamine : None
pyxlsb : None
s3fs : None
scipy : 1.14.0
sqlalchemy : None
tables : 3.9.2
tabulate : None
xarray : None
xlrd : None
zstandard : 0.22.0
tzdata : 2024.1
qtpy : None
pyqt5 : None
@sunghjung3 sunghjung3 added Bug Needs Triage Issue that has not been reviewed by a pandas team member labels Jul 15, 2024
@Animesh-Shukla
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can I take this issue ?

@Animesh-Shukla
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take

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