BUG: DataFrame.iloc.__setitem__ with IntegerArray values (pandas-dev#39040)

Author: jbrockmendel

pandas/core/internals/blocks.py

@@ -984,6 +984,14 @@ def setitem(self, indexer, value):
 
             values = values.astype(arr_value.dtype, copy=False)
 
+        elif is_ea_value:
+            # GH#38952
+            if values.ndim == 1:
+                values[indexer] = value
+            else:
+                # TODO(EA2D): special case not needed with 2D EA
+                values[indexer] = value.to_numpy(values.dtype).reshape(-1, 1)
+
         # set
         else:
             values[indexer] = value

pandas/tests/indexing/test_iloc.py

@@ -14,6 +14,7 @@
     Index,
     NaT,
     Series,
+    array as pd_array,
     concat,
     date_range,
     isna,
@@ -64,6 +65,24 @@ def test_iloc_getitem_list_int(self):
 class TestiLocBaseIndependent:
     """Tests Independent Of Base Class"""
 
+    @pytest.mark.parametrize("box", [pd_array, Series])
+    def test_iloc_setitem_ea_inplace(self, frame_or_series, box):
+        # GH#38952 Case with not setting a full column
+        #  IntegerArray without NAs
+        arr = pd_array([1, 2, 3, 4])
+        obj = frame_or_series(arr.to_numpy("i8"))
+        values = obj.values
+
+        obj.iloc[:2] = box(arr[2:])
+        expected = frame_or_series(np.array([3, 4, 3, 4], dtype="i8"))
+        tm.assert_equal(obj, expected)
+
+        # Check that we are actually in-place
+        if frame_or_series is Series:
+            assert obj.values is values
+        else:
+            assert obj.values.base is values.base and values.base is not None
+
     def test_is_scalar_access(self):
         # GH#32085 index with duplicates doesnt matter for _is_scalar_access
         index = Index([1, 2, 1])