BUG: Pandas 1.4; df.drop method raises an AttributeError when Int64 index is used and index is not unique

[JeremyVriens]

Pandas version checks

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• I have confirmed this bug exists on the main branch of pandas.

Reproducible Example

import pandas as pd

df = pd.DataFrame({"i": pd.Series([1, 2, 2], dtype=pd.Int64Dtype())}).set_index("i")
idx = pd.Index([2])
df.drop(idx)  # Raises AttributeError here

Issue Description

An exception AttributeError: 'BooleanArray' object has no attribute 'nonzero' is raised when the index is Int64 and not unique.

https://github.com/pandas-dev/pandas/blob/main/pandas/core/generic.py#L4345 mask is a BooleanArray here instead of an ndarray when the Index is not unique and of dtype Int64.

It got introduced in 1.4 with this PR: #43760

Expected Behavior

No exception should be raised.

Installed Versions

INSTALLED VERSIONS ------------------ commit : bb1f651 python : 3.8.6.final.0 python-bits : 64 OS : Windows OS-release : 10 Version : 10.0.19041 machine : AMD64 processor : Intel64 Family 6 Model 85 Stepping 4, GenuineIntel byteorder : little LC_ALL : None LANG : None LOCALE : English_United States.1252 pandas : 1.4.0 numpy : 1.22.1 pytz : 2021.3 dateutil : 2.8.2 pip : 22.0.3 setuptools : 59.8.0 Cython : None pytest : 6.2.5 hypothesis : None sphinx : None blosc : None feather : None xlsxwriter : None lxml.etree : None html5lib : None pymysql : None psycopg2 : None jinja2 : 3.0.3 IPython : 8.0.1 pandas_datareader: None bs4 : None bottleneck : None fastparquet : None fsspec : None gcsfs : None matplotlib : None numba : None numexpr : None odfpy : None openpyxl : None pandas_gbq : None pyarrow : None pyreadstat : None pyxlsb : None s3fs : None scipy : None sqlalchemy : 1.4.31 tables : None tabulate : None xarray : None xlrd : None xlwt : None zstandard : None

[simonjayhawkins]

Thanks @JeremyVriens for the report

It got introduced in 1.4 with this PR: #43760

first bad commit: [e750c94] ENH: allow storing ExtensionArrays in Index (#43930)

[simonjayhawkins]

cc @jbrockmendel

[jbrockmendel]

yah its on my radar screen. pd.NA propagation is a PITA.