GH pandas-dev#14499 Panel.ffill ignores axis parameter and fill along axis=1

Author: Tux1

doc/source/whatsnew/v0.19.1.txt

@@ -80,4 +80,6 @@ Bug Fixes
 
 
 - Bug in ``pd.pivot_table`` may raise ``TypeError`` or ``ValueError`` when ``index`` or ``columns``
-  is not scalar and ``values`` is not specified (:issue:`14380`)
+  is not scalar and ``values`` is not specified (:issue:`14380`)
+
+- Bug in ``pd.Panel.ffill`` where ``axis`` was not propagated (:issue:`14499`)

pandas/core/generic.py

@@ -3208,7 +3208,10 @@ def fillna(self, value=None, method=None, axis=None, inplace=False,
         # set the default here, so functions examining the signaure
         # can detect if something was set (e.g. in groupby) (GH9221)
         if axis is None:
-            axis = 0
+            if self.ndim == 3:
+                axis = 1
+            else:
+                axis = 0
         axis = self._get_axis_number(axis)
         method = missing.clean_fill_method(method)
 
@@ -3233,9 +3236,13 @@ def fillna(self, value=None, method=None, axis=None, inplace=False,
 
             # 3d
             elif self.ndim == 3:
-
+                if axis == 0:
+                    raise NotImplementedError('Cannot fillna with axis=0 '
+                                              'for Panel')
                 # fill in 2d chunks
-                result = dict([(col, s.fillna(method=method, value=value))
+                result = dict([(col, s.fillna(method=method, 
+                                              value=value, 
+                                              axis=axis-1))
                                for col, s in self.iteritems()])
                 new_obj = self._constructor.\
                     from_dict(result).__finalize__(self)

pandas/tests/test_panel.py

@@ -1519,6 +1519,37 @@ def test_ffill_bfill(self):
         assert_panel_equal(self.panel.bfill(),
                            self.panel.fillna(method='bfill'))
 
+    def test_ffill_bfill_axis(self):
+        #GH 14499
+        a = Panel({
+            'a':np.arange(15, dtype=float).reshape((5, 3)), 
+            'b':np.arange(15, 30, dtype=float).reshape((5, 3))
+        })
+        f1 = a.copy()
+        f2 = a.copy()
+        b1 = a.copy()
+        b2 = a.copy()
+        a['a'].loc[1, 1] = np.nan
+        f1['a'].loc[1, 1] = 1
+        f2['a'].loc[1, 1] = 3
+        b1['a'].loc[1, 1] = 7
+        b2['a'].loc[1, 1] = 5
+        # method='ffill'
+        # axis=1
+        assert_panel_equal(a.ffill(axis=1), f1)
+
+        # method='ffill'
+        # axis=2
+        assert_panel_equal(a.ffill(axis=2), f2)
+
+        # method='bfill'
+        # axis=1
+        assert_panel_equal(a.bfill(axis=1), b1)
+
+        # method='bfill'
+        # axis=2
+        assert_panel_equal(a.bfill(axis=2), b2)
+
     def test_truncate_fillna_bug(self):
         # #1823
         result = self.panel.truncate(before=None, after=None, axis='items')