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Description
Pandas version checks
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I have checked that this issue has not already been reported.
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I have confirmed this bug exists on the latest version of pandas.
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I have confirmed this bug exists on the main branch of pandas.
Reproducible Example
import pandas as pd
import numpy as np
s = pd.Series()
a = np.array([1])
a2 = np.array([0,1])
assert a.shape == (1,) #array is 1 dimensional with 1 element
s['whatever'] = a
assert s['whatever'].shape == a.shape #expected
s['whatever'] = a
print("shape after reassignment: ", s['whatever'].shape) #prints '()'
assert s['whatever'].shape == a.shape # FAILS HERE
s['whatever'] = a2
assert a2.shape ==(2,)
assert s['whatever'].shape == a2.shape #works for arrays with more than one element as expectedIssue Description
When reassigning a value to an index in a series, if the value is a numpy array with a single element, the dimension of the array is lost. When assigning to an index that does not exist, the array retains it's shape (1,)
Expected Behavior
The array's shape shouldn't depend on whether the index already exists in the series or not. This was the behavior in pandas 2.0.0.
Installed Versions
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commit : 965ceca9fd796940050d6fc817707bba1c4f9bff
python : 3.10.10.final.0
python-bits : 64
OS : Linux
OS-release : 5.15.96-0-virt
Version : #1-Alpine SMP Sun, 26 Feb 2023 15:14:12 +0000
machine : x86_64
processor :
byteorder : little
LC_ALL : None
LANG : C.UTF-8
LOCALE : en_US.UTF-8
pandas : 2.0.2
numpy : 1.24.3
pytz : 2023.3
dateutil : 2.8.2
setuptools : 67.6.1
pip : 23.1
Cython : 0.29.35
pytest : 7.3.1
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.1.2
IPython : 8.12.0
pandas_datareader: None
bs4 : None
bottleneck : None
brotli : None
fastparquet : None
fsspec : 2023.4.0
gcsfs : 2023.4.0
matplotlib : 3.7.1
numba : 0.57.0
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : 11.0.0
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : 1.10.1
snappy : None
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
zstandard : None
tzdata : 2023.3
qtpy : None
pyqt5 : None