Backport PR #54913 on branch 2.1.x (REGR: drop_duplicates raising for arrow strings)

doc/source/whatsnew/v2.1.1.rst

@@ -16,6 +16,7 @@ Fixed regressions
 - Fixed regression in :func:`merge` when merging over a PyArrow string index (:issue:`54894`)
 - Fixed regression in :func:`read_csv` when ``usecols`` is given and ``dtypes`` is a dict for ``engine="python"`` (:issue:`54868`)
 - Fixed regression in :meth:`DataFrame.__setitem__` raising ``AssertionError`` when setting a :class:`Series` with a partial :class:`MultiIndex` (:issue:`54875`)
+- Fixed regression in :meth:`Series.drop_duplicates` for PyArrow strings (:issue:`54904`)
 - Fixed regression in :meth:`Series.value_counts` raising for numeric data if ``bins`` was specified (:issue:`54857`)
 - Fixed regression when comparing a :class:`Series` with ``datetime64`` dtype with ``None`` (:issue:`54870`)
 

pandas/core/algorithms.py

@@ -1000,7 +1000,7 @@ def duplicated(
  duplicated : ndarray[bool]
  """
  if hasattr(values, "dtype"):
- if isinstance(values.dtype, ArrowDtype):
+ if isinstance(values.dtype, ArrowDtype) and values.dtype.kind in "ifub":
  values = values._to_masked() # type: ignore[union-attr]
 
  if isinstance(values.dtype, BaseMaskedDtype):

pandas/tests/series/methods/test_drop_duplicates.py

@@ -1,6 +1,7 @@
 import numpy as np
 import pytest
 
+import pandas as pd
 from pandas import (
  Categorical,
  Series,
@@ -256,3 +257,11 @@ def test_duplicated_arrow_dtype(self):
  result = ser.drop_duplicates()
  expected = Series([True, False, None], dtype="bool[pyarrow]")
  tm.assert_series_equal(result, expected)
+
+ def test_drop_duplicates_arrow_strings(self):
+ # GH#54904
+ pa = pytest.importorskip("pyarrow")
+ ser = Series(["a", "a"], dtype=pd.ArrowDtype(pa.string()))
+ result = ser.drop_duplicates()
+ expecetd = Series(["a"], dtype=pd.ArrowDtype(pa.string()))
+ tm.assert_series_equal(result, expecetd)