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BUG: pd.unique(index) does not always return an index #57043
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Thanks for the report, confirmed on main. Further investigations and PRs to fix are welcome! |
Hi, I found that >>> print(pd.Index([pd.Timestamp("20160101", tz="US/Eastern")]).dtype.__class__)
<class 'pandas.core.dtypes.dtypes.DatetimeTZDtype'>
>>> print(pd.Index([pd.Timestamp("20160101")]).dtype.__class__)
<class 'numpy.dtypes.DateTime64DType'>
>>> print(pd.Index([1]).dtype.__class__)
<class 'numpy.dtypes.Int64DType'> Therefore, in Here are the lines in pandas/pandas/core/algorithms.py Lines 433 to 442 in d928a5c
|
It is possible to resolve the issue if we provide the dtype or dtype string alias manually to >>> pd.unique(pd.Index([pd.Timestamp("20160101")], dtype='datetime64[ns, US/Eastern]'))
DatetimeIndex(['2016-01-01 00:00:00-05:00'], dtype='datetime64[ns, US/Eastern]', freq=None)
>>> pd.unique(pd.Index([1], dtype='Int32'))
Index([1], dtype='Int32') |
Pandas version checks
I have checked that this issue has not already been reported.
I have confirmed this bug exists on the latest version of pandas.
I have confirmed this bug exists on the main branch of pandas.
Reproducible Example
Issue Description
pd.unique
documentation says the return value isIndex : when the input is an Index
, but the return value is sometimes a numpy array.Expected Behavior
pd.unique
should return an index of the same type as the one provided to it.Installed Versions
INSTALLED VERSIONS
commit : fd3f571
python : 3.9.18.final.0
python-bits : 64
OS : Darwin
OS-release : 23.2.0
Version : Darwin Kernel Version 23.2.0: Wed Nov 15 21:55:06 PST 2023; root:xnu-10002.61.3~2/RELEASE_ARM64_T6020
machine : arm64
processor : arm
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8
pandas : 2.2.0
numpy : 1.26.3
pytz : 2023.3.post1
dateutil : 2.8.2
setuptools : 68.2.2
pip : 23.3.1
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 : 8.18.1
pandas_datareader : None
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : None
bottleneck : None
dataframe-api-compat : None
fastparquet : None
fsspec : None
gcsfs : None
matplotlib : None
numba : None
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : None
pyreadstat : None
python-calamine : None
pyxlsb : None
s3fs : None
scipy : None
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
zstandard : None
tzdata : 2023.4
qtpy : None
pyqt5 : None
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