BUG: df.fillna ignores axis when df is single block (#47714)

* Update generic.py * Update test_fillna.py * Update v1.5.0.rst * fix array format * fix what's new description * fix format * Update test_fillna.py

Author: GYHHAHA

doc/source/whatsnew/v1.5.0.rst

@@ -914,6 +914,7 @@ Missing
 - Bug in :meth:`Series.fillna` and :meth:`DataFrame.fillna` with :class:`IntervalDtype` and incompatible value raising instead of casting to a common (usually object) dtype (:issue:`45796`)
 - Bug in :meth:`DataFrame.interpolate` with object-dtype column not returning a copy with ``inplace=False`` (:issue:`45791`)
 - Bug in :meth:`DataFrame.dropna` allows to set both ``how`` and ``thresh`` incompatible arguments (:issue:`46575`)
+- Bug in :meth:`DataFrame.fillna` ignored ``axis`` when :class:`DataFrame` is single block (:issue:`47713`)
 
 MultiIndex
 ^^^^^^^^^^

pandas/core/generic.py

@@ -6679,7 +6679,7 @@ def fillna(
  return result if not inplace else None
 
  elif not is_list_like(value):
- if not self._mgr.is_single_block and axis == 1:
+ if axis == 1:
 
  result = self.T.fillna(value=value, limit=limit).T
 

pandas/tests/frame/methods/test_fillna.py

@@ -685,6 +685,29 @@ def test_inplace_dict_update_view(self, val):
  tm.assert_frame_equal(df, expected)
  tm.assert_frame_equal(result_view, expected)
 
+ def test_single_block_df_with_horizontal_axis(self):
+ # GH 47713
+ df = DataFrame(
+ {
+ "col1": [5, 0, np.nan, 10, np.nan],
+ "col2": [7, np.nan, np.nan, 5, 3],
+ "col3": [12, np.nan, 1, 2, 0],
+ "col4": [np.nan, 1, 1, np.nan, 18],
+ }
+ )
+ result = df.fillna(50, limit=1, axis=1)
+ expected = DataFrame(
+ [
+ [5.0, 7.0, 12.0, 50.0],
+ [0.0, 50.0, np.nan, 1.0],
+ [50.0, np.nan, 1.0, 1.0],
+ [10.0, 5.0, 2.0, 50.0],
+ [50.0, 3.0, 0.0, 18.0],
+ ],
+ columns=["col1", "col2", "col3", "col4"],
+ )
+ tm.assert_frame_equal(result, expected)
+
 
 def test_fillna_nonconsolidated_frame():
  # https://github.com/pandas-dev/pandas/issues/36495