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Reproducible Example

import pandas as pd
df = pd.DataFrame([1,2],index=pd.MultiIndex.from_tuples([(1,1),(1,pd.NA)]))

df.sort_index()
#        0
# 1 1    1
#   NaN  2

df.sort_index(level=[0,1])
#        0
# 1 NaN  2
#   1    1

# na_position seems to be ignored
df.sort_index(level=[0,1],na_position="last")
#        0
# 1 NaN  2
#   1    1

Issue Description

Sorting should be consistent whether or not all levels in level kwarg are provided. It appears that na_position is ignored when providing level.

Expected Behavior

na_position="last" should be the default behaviour no matter whether level is provided or not

Installed Versions

INSTALLED VERSIONS ------------------ commit : b69bd0755d654c0dba42042df7b2251918274327 python : 3.10.4.final.0 python-bits : 64 OS : Linux OS-release : 6.0.12-76060006-generic Version : #202212290932~1674139725~22.04~ca93ccf SMP PREEMPT_DYNAMIC Thu J machine : x86_64 processor : x86_64 byteorder : little LC_ALL : None LANG : en_US.UTF-8 LOCALE : en_US.UTF-8 pandas : 2.1.0.dev0+47.gb69bd0755d numpy : 1.23.5 pytz : 2022.7.1 dateutil : 2.8.2 setuptools : 65.6.3 pip : 23.0 Cython : None pytest : 7.2.0 hypothesis : None sphinx : None blosc : None feather : None xlsxwriter : None lxml.etree : None html5lib : None pymysql : None psycopg2 : None jinja2 : 3.1.2 IPython : 8.8.0 pandas_datareader: None bs4 : 4.11.1 bottleneck : None brotli : None fastparquet : None fsspec : 2022.11.0 gcsfs : None matplotlib : 3.6.2 numba : 0.56.4 numexpr : None odfpy : None openpyxl : None pandas_gbq : None pyarrow : None pyreadstat : None pyxlsb : None s3fs : 2022.11.0 scipy : 1.9.3 snappy : None sqlalchemy : None tables : None tabulate : None xarray : None xlrd : None zstandard : None tzdata : None qtpy : None pyqt5 : None

Comment From: dannyi96

seems like this is the expected behavior as of now. As per docs - https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.sort_index.html

na_position{‘first’, ‘last’}, default ‘last’
Puts NaNs at the beginning if first; last puts NaNs at the end. Not implemented for MultiIndex.

Could be a possible enhancement though I guess.

Comment From: phofl

Yeah, can you rephrase as enhancement request?

Comment From: AlexKirko

At the very least, it would be nice to give the user a warning in this case, as there is little reason for them to expect the argument being ignored.

Comment From: phofl

I'd prefer an implementation. Alternatively I'd rather raise than warn