BUG: Dataframe init constructor fills with NaN when index = MultiIndex

[joseortiz3]

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

import pandas as pd

series1 = pd.Series(data=[1,2], index=['A','B'])
series2 = pd.Series(data=[3,4], index=['A','B'])

df = pd.DataFrame({'s1': series1, 's2': series2})
index = pd.MultiIndex.from_product([['C'],['A','B']])
df.index = index

# df is
# | |s1|s2|
#C|A| 1| 3|
# |B| 2| 4|


df2 = pd.DataFrame({'s1': series1, 's2': series2}, index=index)

# df2 is
# | | s1| s2|
#C|A|NaN|NaN|
# |B|NaN|NaN|

Issue Description

Dataframe fills with NaN when the Dataframe init / constructor is passed a MultiIndex for the index argument (as in df2). Only workaround is to replace the index after the dataframe is initialized (as in df).

Example: df is fine above, but df2 is filled with NaN.

Expected Behavior

df2 and df should be the same above.

Installed Versions

INSTALLED VERSIONS

commit : 0691c5c
python : 3.10.11.final.0
python-bits : 64
OS : Windows
OS-release : 10
Version : 10.0.22631
machine : AMD64
processor : AMD64 Family 25 Model 33 Stepping 0, AuthenticAMD
byteorder : little
LC_ALL : None
LANG : None
LOCALE : English_United States.1252

pandas : 2.2.3
numpy : 1.23.5
pytz : 2023.3
dateutil : 2.8.2
setuptools : 65.5.0
pip : 24.2
Cython : 0.29.34
pytest : 7.4.2
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : 5.3.0
html5lib : 1.1
pymysql : None
psycopg2 : 2.9.9
jinja2 : 3.1.2
IPython : 8.12.0
pandas_datareader : None
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : 4.12.3
bottleneck : None
dataframe-api-compat : None
fastparquet : 2023.2.0
fsspec : 2023.4.0
gcsfs : None
matplotlib : 3.7.1
numba : 0.56.4
numexpr : 2.8.4
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : 11.0.0
pyreadstat : None
python-calamine : None
pyxlsb : None
s3fs : None
scipy : 1.10.1
sqlalchemy : 2.0.9
tables : 3.8.0
tabulate : 0.9.0
xarray : None
xlrd : None
zstandard : None
tzdata : 2023.3
qtpy : None
pyqt5 : None

[KarnatiVr]

@joseortiz3 can you assign this to me?

[rhshadrach]

Thanks for the report. This is behaving as documented:

https://pandas.pydata.org/docs/dev/reference/api/pandas.DataFrame.html

If a dict contains Series which have an index defined, it is aligned by its index. This alignment also occurs if data is a Series or a DataFrame itself. Alignment is done on Series/DataFrame inputs.

Also see the last example on that page.