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
from io import StringIO
sr = pandas.read_csv(StringIO(',z,a\nt,1.0,\nr,,5.0\ns,2.0,\nz,,2.0\nv,,4.0\nr,3.0,\n'),index_col=0).stack()
print(sr)
print(sr.unstack())
print(sr.unstack(sort=False))Issue Description
the original series is
t z 1.0
r a 5.0
s z 2.0
z a 2.0
v a 4.0
r z 3.0
dtype: float64
the default unstack() call returns a dataframe sorted on the index
z a
r 3.0 5.0
s 2.0 NaN
t 1.0 NaN
v NaN 4.0
z NaN 2.0
while using the sort argument unstack(sort=False) gives wrong results yet a the dataframe index keeps the original order
z a
t 1.0 5.0
r 2.0 NaN
s 2.0 NaN
z NaN 4.0
v NaN 3.0
Expected Behavior
I would expect to get the dataframe with the index in the its original order but with the proper results
z a
t 1.0 NaN
r 3.0 5.0
s 2.0 NaN
z NaN 2.0
v NaN 4.0
(I can get this result with sr.unstack().reindex(sr.index.get_level_values(0).unique()))
Installed Versions
INSTALLED VERSIONS
commit : e86ed37
python : 3.11.6.final.0
python-bits : 64
OS : Windows
OS-release : 10
Version : 10.0.19045
machine : AMD64
processor : AMD64 Family 23 Model 96 Stepping 1, AuthenticAMD
byteorder : little
LC_ALL : None
LANG : None
LOCALE : English_Belgium.1252
pandas : 2.1.1
numpy : 1.26.0
pytz : 2023.3.post1
dateutil : 2.8.2
setuptools : 60.2.0
pip : 23.2.1
Cython : 0.29.36
pytest : None
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.1.2
IPython : 8.16.1
pandas_datareader : None
bs4 : 4.12.2
bottleneck : None
dataframe-api-compat: None
fastparquet : None
fsspec : None
gcsfs : None
matplotlib : 3.8.0
numba : None
numexpr : None
odfpy : None
openpyxl : 3.1.2
pandas_gbq : None
pyarrow : None
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : None
sqlalchemy : 2.0.21
tables : None
tabulate : None
xarray : None
xlrd : None
zstandard : None
tzdata : 2023.3
qtpy : None
pyqt5 : None