ENH: Make get_dummies return ea booleans for ea inputs (#56291)

* ENH: Make get_dummies return ea booleans for ea inputs

* ENH: Make get_dummies return ea booleans for ea inputs

* Update

* Update pandas/tests/reshape/test_get_dummies.py

Co-authored-by: Thomas Baumann <[email protected]>

* Update test_get_dummies.py

* Update test_get_dummies.py

* Fixup

---------

Co-authored-by: Thomas Baumann <[email protected]>

Author: phofl

doc/source/whatsnew/v2.2.0.rst

@@ -218,6 +218,7 @@ Other enhancements
 
 - :meth:`~DataFrame.to_sql` with method parameter set to ``multi`` works with Oracle on the backend
 - :attr:`Series.attrs` / :attr:`DataFrame.attrs` now uses a deepcopy for propagating ``attrs`` (:issue:`54134`).
+- :func:`get_dummies` now returning  extension dtypes ``boolean`` or ``bool[pyarrow]`` that are compatible with the input dtype (:issue:`56273`)
 - :func:`read_csv` now supports ``on_bad_lines`` parameter with ``engine="pyarrow"``. (:issue:`54480`)
 - :func:`read_sas` returns ``datetime64`` dtypes with resolutions better matching those stored natively in SAS, and avoids returning object-dtype in cases that cannot be stored with ``datetime64[ns]`` dtype (:issue:`56127`)
 - :func:`read_spss` now returns a :class:`DataFrame` that stores the metadata in :attr:`DataFrame.attrs`. (:issue:`54264`)

pandas/core/reshape/encoding.py

@@ -21,9 +21,14 @@
     is_object_dtype,
     pandas_dtype,
 )
+from pandas.core.dtypes.dtypes import (
+    ArrowDtype,
+    CategoricalDtype,
+)
 
 from pandas.core.arrays import SparseArray
 from pandas.core.arrays.categorical import factorize_from_iterable
+from pandas.core.arrays.string_ import StringDtype
 from pandas.core.frame import DataFrame
 from pandas.core.indexes.api import (
     Index,
@@ -244,8 +249,25 @@ def _get_dummies_1d(
     # Series avoids inconsistent NaN handling
     codes, levels = factorize_from_iterable(Series(data, copy=False))
 
-    if dtype is None:
+    if dtype is None and hasattr(data, "dtype"):
+        input_dtype = data.dtype
+        if isinstance(input_dtype, CategoricalDtype):
+            input_dtype = input_dtype.categories.dtype
+
+        if isinstance(input_dtype, ArrowDtype):
+            import pyarrow as pa
+
+            dtype = ArrowDtype(pa.bool_())  # type: ignore[assignment]
+        elif (
+            isinstance(input_dtype, StringDtype)
+            and input_dtype.storage != "pyarrow_numpy"
+        ):
+            dtype = pandas_dtype("boolean")  # type: ignore[assignment]
+        else:
+            dtype = np.dtype(bool)
+    elif dtype is None:
         dtype = np.dtype(bool)
+
     _dtype = pandas_dtype(dtype)
 
     if is_object_dtype(_dtype):

pandas/tests/reshape/test_get_dummies.py

@@ -4,13 +4,18 @@
 import numpy as np
 import pytest
 
+import pandas.util._test_decorators as td
+
 from pandas.core.dtypes.common import is_integer_dtype
 
 import pandas as pd
 from pandas import (
+    ArrowDtype,
     Categorical,
+    CategoricalDtype,
     CategoricalIndex,
     DataFrame,
+    Index,
     RangeIndex,
     Series,
     SparseDtype,
@@ -19,6 +24,11 @@
 import pandas._testing as tm
 from pandas.core.arrays.sparse import SparseArray
 
+try:
+    import pyarrow as pa
+except ImportError:
+    pa = None
+
 
 class TestGetDummies:
     @pytest.fixture
@@ -217,6 +227,7 @@ def test_dataframe_dummies_string_dtype(self, df):
             },
             dtype=bool,
         )
+        expected[["B_b", "B_c"]] = expected[["B_b", "B_c"]].astype("boolean")
         tm.assert_frame_equal(result, expected)
 
     def test_dataframe_dummies_mix_default(self, df, sparse, dtype):
@@ -693,3 +704,37 @@ def test_get_dummies_ea_dtype_dataframe(self, any_numeric_ea_and_arrow_dtype):
             dtype=any_numeric_ea_and_arrow_dtype,
         )
         tm.assert_frame_equal(result, expected)
+
+    @td.skip_if_no("pyarrow")
+    def test_get_dummies_ea_dtype(self):
+        # GH#56273
+        for dtype, exp_dtype in [
+            ("string[pyarrow]", "boolean"),
+            ("string[pyarrow_numpy]", "bool"),
+            (CategoricalDtype(Index(["a"], dtype="string[pyarrow]")), "boolean"),
+            (CategoricalDtype(Index(["a"], dtype="string[pyarrow_numpy]")), "bool"),
+        ]:
+            df = DataFrame({"name": Series(["a"], dtype=dtype), "x": 1})
+            result = get_dummies(df)
+            expected = DataFrame({"x": 1, "name_a": Series([True], dtype=exp_dtype)})
+            tm.assert_frame_equal(result, expected)
+
+    @td.skip_if_no("pyarrow")
+    def test_get_dummies_arrow_dtype(self):
+        # GH#56273
+        df = DataFrame({"name": Series(["a"], dtype=ArrowDtype(pa.string())), "x": 1})
+        result = get_dummies(df)
+        expected = DataFrame({"x": 1, "name_a": Series([True], dtype="bool[pyarrow]")})
+        tm.assert_frame_equal(result, expected)
+
+        df = DataFrame(
+            {
+                "name": Series(
+                    ["a"],
+                    dtype=CategoricalDtype(Index(["a"], dtype=ArrowDtype(pa.string()))),
+                ),
+                "x": 1,
+            }
+        )
+        result = get_dummies(df)
+        tm.assert_frame_equal(result, expected)