BUG: add a whatsnew entry in v0.24.0 / bug fixes / reshaping

Also
- move test close to test_where_none`
- reformat test as asked in PR

Author: pajachiet

doc/source/whatsnew/v0.24.0.txt

@@ -487,7 +487,7 @@ Reshaping
 - Bug in :func:`pandas.concat` when joining resampled DataFrames with timezone aware index (:issue:`13783`)
 - Bug in :meth:`Series.combine_first` with ``datetime64[ns, tz]`` dtype which would return tz-naive result (:issue:`21469`)
 - Bug in :meth:`Series.where` and :meth:`DataFrame.where` with ``datetime64[ns, tz]`` dtype (:issue:`21546`)
--
+- Bug in :meht:`Dataframe.where` with empty ``df`` and empty ``cond`` having non bool dtype (:pr:`21947`)
 -
 
 Build Changes

pandas/tests/frame/test_indexing.py

@@ -2773,6 +2773,16 @@ def test_where_none(self):
                                     'on mixed-type'):
             df.where(~isna(df), None, inplace=True)
 
+    def test_where_empty_df_and_empty_cond_having_non_bool_dtypes(self):
+        # GH 21947
+        df = pd.DataFrame(columns=['a'])
+        cond = df.applymap(lambda x: x > 0)
+        # Should not raise ValueError:
+        # Boolean array expected for the condition, not object
+        result = df.where(cond)
+        expected = df
+        tm.assert_frame_equal(expected, result)
+
     def test_where_align(self):
 
         def create():
@@ -2939,15 +2949,6 @@ def test_where_callable(self):
         tm.assert_frame_equal(result,
                               (df + 2).where((df + 2) > 8, (df + 2) + 10))
 
-    def test_where_empty_df_and_empty_cond_having_non_bool_dtypes(self):
-        # GH 21947
-        data = []
-        df = pd.DataFrame(columns=['a'], data=data)
-        cond = df.applymap(lambda x: x > 0)
-        # Should not raise ValueError:
-        # Boolean array expected for the condition, not object
-        df.where(cond)
-
     def test_where_tz_values(self, tz_naive_fixture):
         df1 = DataFrame(DatetimeIndex(['20150101', '20150102', '20150103'],
                                       tz=tz_naive_fixture),