[ArrayManager] Enable downcast in fillna / enable where indexing tests (pandas-dev#39697)

Author: jorisvandenbossche

.github/workflows/ci.yml

@@ -154,7 +154,9 @@ jobs:
         source activate pandas-dev
         pytest pandas/tests/frame/methods --array-manager
 
-        # indexing iset related (temporary since other tests don't pass yet)
+        # indexing subset (temporary since other tests don't pass yet)
+        pytest pandas/tests/frame/indexing/test_indexing.py::TestDataFrameIndexing::test_setitem_boolean --array-manager
+        pytest pandas/tests/frame/indexing/test_where.py --array-manager
         pytest pandas/tests/frame/indexing/test_indexing.py::TestDataFrameIndexing::test_setitem_multi_index --array-manager
         pytest pandas/tests/frame/indexing/test_setitem.py::TestDataFrameSetItem::test_setitem_listlike_indexer_duplicate_columns --array-manager
         pytest pandas/tests/indexing/multiindex/test_setitem.py::TestMultiIndexSetItem::test_astype_assignment_with_dups --array-manager

pandas/core/internals/array_manager.py

@@ -7,7 +7,7 @@
 
 import numpy as np
 
-from pandas._libs import algos as libalgos, lib
+from pandas._libs import lib
 from pandas._typing import ArrayLike, DtypeObj, Hashable
 from pandas.util._validators import validate_bool_kwarg
 
@@ -377,28 +377,9 @@ def shift(self, periods: int, axis: int, fill_value) -> ArrayManager:
         )
 
     def fillna(self, value, limit, inplace: bool, downcast) -> ArrayManager:
-        # TODO implement downcast
-        inplace = validate_bool_kwarg(inplace, "inplace")
-
-        def array_fillna(array, value, limit, inplace):
-
-            mask = isna(array)
-            if limit is not None:
-                limit = libalgos.validate_limit(None, limit=limit)
-                mask[mask.cumsum() > limit] = False
-
-            # TODO could optimize for arrays that cannot hold NAs
-            # (like _can_hold_na on Blocks)
-            if not inplace:
-                array = array.copy()
-
-            # np.putmask(array, mask, value)
-            if np.any(mask):
-                # TODO allow invalid value if there is nothing to fill?
-                array[mask] = value
-            return array
-
-        return self.apply(array_fillna, value=value, limit=limit, inplace=inplace)
+        return self.apply_with_block(
+            "fillna", value=value, limit=limit, inplace=inplace, downcast=downcast
+        )
 
     def downcast(self) -> ArrayManager:
         return self.apply_with_block("downcast")
@@ -454,7 +435,7 @@ def is_mixed_type(self) -> bool:
 
     @property
     def is_numeric_mixed_type(self) -> bool:
-        return False
+        return all(is_numeric_dtype(t) for t in self.get_dtypes())
 
     @property
     def any_extension_types(self) -> bool:

pandas/tests/frame/indexing/test_where.py

@@ -499,6 +499,7 @@ def test_where_axis(self):
         assert return_value is None
         tm.assert_frame_equal(result, expected)
 
+    def test_where_axis_multiple_dtypes(self):
         # Multiple dtypes (=> multiple Blocks)
         df = pd.concat(
             [