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
ix = pd.MultiIndex.from_tuples([('a', '10'), ('a', '18'), ('a', '25'), ('b', '16'), ('b', '26'), ('a', '45'), ('b', '28'), ('a', '5'), ('a', '50'), ('a', '51'), ('b', '4'), ('b', '49'), ('a', '78'), ('a', '81'), ('a', '85'),('b', '67'),('b', '74'), ('b', '77'), ('b', '83'),('b', '97')], names=['group', 'str'])
df = pd.DataFrame({'x':range(len(ix))},index=ix)
df.sort_index() # Works
df2 = df.iloc[0:6]
df2.sort_index() # Doesn't sort right
df2.index.sort_values() # Sorts correctly
df3 = df.iloc[0:7]
df3.sort_index() # Works!
df4 = df.iloc[1:7]
df4.sort_index() # Doesn't sort rightIssue Description
df2.sort_index() should sort but it doesn't. It doesn't leave things the way it is either though it does a weird half sort.
I get:
In [30]: df2
Out[30]:
x
group str
a 10 0
18 1
25 2
b 16 3
26 4
a 45 5
In [31]: df2.sort_index()
Out[31]:
x
group str
a 10 0
18 1
25 2
b 16 3
a 45 5
b 26 4This was discovered while trying to debug why Beam tests weren't working right under Pandas 2.1. I can't get this bug to reproduce when I start with the first 6 elements of ix when making df, for some reason I have to have a longer index to start it off.
Note that this works in 2.0.3.
Expected Behavior
The index should be sorted, the same way it is for df2.index.sort_values()
Installed Versions
INSTALLED VERSIONS
commit : e86ed37
python : 3.11.5.final.0
python-bits : 64
OS : Linux
OS-release : 6.3.11-1rodete2-amd64
Version : #1 SMP PREEMPT_DYNAMIC Debian 6.3.11-1rodete2 (2023-08-24)
machine : x86_64
processor :
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8
pandas : 2.1.1
numpy : 1.24.4
pytz : 2023.3.post1
dateutil : 2.8.2
setuptools : 68.2.2
pip : 23.2.1
Cython : None
pytest : 7.4.2
hypothesis : 6.84.3
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : 1.4.6
psycopg2 : 2.9.7
jinja2 : None
IPython : 8.15.0
pandas_datareader : 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 : 11.0.0
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : 1.11.2
sqlalchemy : 1.4.49
tables : None
tabulate : None
xarray : None
xlrd : None
zstandard : 0.21.0
tzdata : 2023.3
qtpy : None
pyqt5 : None