BUG: Reindex casting to object in certain situation

doc/source/whatsnew/v1.6.0.rst

@@ -152,6 +152,7 @@ Interval
 Indexing
 ^^^^^^^^
 - Bug in :meth:`DataFrame.reindex` filling with wrong values when indexing columns and index for ``uint`` dtypes (:issue:`48184`)
+- Bug in :meth:`DataFrame.reindex` casting dtype to ``object`` when :class:`DataFrame` has single extension array column when indexing columns and index (:issue:`48190`)
 -
 
 Missing

pandas/core/generic.py

@@ -5345,6 +5345,9 @@ def _needs_reindex_multi(self, axes, method, level) -> bool_t:
             and method is None
             and level is None
             and not self._is_mixed_type
+            and not (
+                len(self.dtypes) == 1 and is_extension_array_dtype(self.dtypes.iloc[0])
+            )
         )
 
     def _reindex_multi(self, axes, copy, fill_value):

pandas/tests/frame/methods/test_reindex.py

@@ -782,6 +782,15 @@ def test_reindex_uint_dtypes_fill_value(self, any_unsigned_int_numpy_dtype):
         )
         tm.assert_frame_equal(result, expected)
 
+    def test_reindex_single_column_ea_index_and_columns(self, any_numeric_ea_dtype):
+        # GH#48190
+        df = DataFrame({"a": [1, 2]}, dtype=any_numeric_ea_dtype)
+        result = df.reindex(columns=list("ab"), index=[0, 1, 2], fill_value=10)
+        expected = DataFrame(
+            {"a": Series([1, 2, 10], dtype=any_numeric_ea_dtype), "b": 10}
+        )
+        tm.assert_frame_equal(result, expected)
+
     def test_reindex_dups(self):
 
         # GH4746, reindex on duplicate index error messages