ENH: Add ea support to get_dummies (#50849)

* ENH: Add ea support to get_dummies

* Fix mypy

Author: phofl

doc/source/whatsnew/v2.0.0.rst

@@ -160,6 +160,7 @@ Other enhancements
 - Added ``name`` parameter to :meth:`IntervalIndex.from_breaks`, :meth:`IntervalIndex.from_arrays` and :meth:`IntervalIndex.from_tuples` (:issue:`48911`)
 - Improve exception message when using :func:`assert_frame_equal` on a :class:`DataFrame` to include the column that is compared (:issue:`50323`)
 - Improved error message for :func:`merge_asof` when join-columns were duplicated (:issue:`50102`)
+- Added support for extension array dtypes to :func:`get_dummies` (:func:`32430`)
 - Added :meth:`Index.infer_objects` analogous to :meth:`Series.infer_objects` (:issue:`50034`)
 - Added ``copy`` parameter to :meth:`Series.infer_objects` and :meth:`DataFrame.infer_objects`, passing ``False`` will avoid making copies for series or columns that are already non-object or where no better dtype can be inferred (:issue:`50096`)
 - :meth:`DataFrame.plot.hist` now recognizes ``xlabel`` and ``ylabel`` arguments (:issue:`49793`)

pandas/core/reshape/encoding.py

@@ -16,6 +16,7 @@
     is_integer_dtype,
     is_list_like,
     is_object_dtype,
+    pandas_dtype,
 )
 
 from pandas.core.arrays import SparseArray
@@ -240,9 +241,9 @@ def _get_dummies_1d(
 
     if dtype is None:
         dtype = np.dtype(bool)
-    dtype = np.dtype(dtype)
+    _dtype = pandas_dtype(dtype)
 
-    if is_object_dtype(dtype):
+    if is_object_dtype(_dtype):
         raise ValueError("dtype=object is not a valid dtype for get_dummies")
 
     def get_empty_frame(data) -> DataFrame:
@@ -317,7 +318,12 @@ def get_empty_frame(data) -> DataFrame:
 
     else:
         # take on axis=1 + transpose to ensure ndarray layout is column-major
-        dummy_mat = np.eye(number_of_cols, dtype=dtype).take(codes, axis=1).T
+        eye_dtype: NpDtype
+        if isinstance(_dtype, np.dtype):
+            eye_dtype = _dtype
+        else:
+            eye_dtype = np.bool_
+        dummy_mat = np.eye(number_of_cols, dtype=eye_dtype).take(codes, axis=1).T
 
         if not dummy_na:
             # reset NaN GH4446
@@ -327,7 +333,7 @@ def get_empty_frame(data) -> DataFrame:
             # remove first GH12042
             dummy_mat = dummy_mat[:, 1:]
             dummy_cols = dummy_cols[1:]
-        return DataFrame(dummy_mat, index=index, columns=dummy_cols)
+        return DataFrame(dummy_mat, index=index, columns=dummy_cols, dtype=_dtype)
 
 
 def from_dummies(

pandas/tests/reshape/test_get_dummies.py

@@ -657,3 +657,23 @@ def test_get_dummies_with_string_values(self, values):
 
         with pytest.raises(TypeError, match=msg):
             get_dummies(df, columns=values)
+
+    def test_get_dummies_ea_dtype_series(self, any_numeric_ea_dtype):
+        # GH#32430
+        ser = Series(list("abca"))
+        result = get_dummies(ser, dtype=any_numeric_ea_dtype)
+        expected = DataFrame(
+            {"a": [1, 0, 0, 1], "b": [0, 1, 0, 0], "c": [0, 0, 1, 0]},
+            dtype=any_numeric_ea_dtype,
+        )
+        tm.assert_frame_equal(result, expected)
+
+    def test_get_dummies_ea_dtype_dataframe(self, any_numeric_ea_dtype):
+        # GH#32430
+        df = DataFrame({"x": list("abca")})
+        result = get_dummies(df, dtype=any_numeric_ea_dtype)
+        expected = DataFrame(
+            {"x_a": [1, 0, 0, 1], "x_b": [0, 1, 0, 0], "x_c": [0, 0, 1, 0]},
+            dtype=any_numeric_ea_dtype,
+        )
+        tm.assert_frame_equal(result, expected)