ENH: Allow fill_value for frame arithmetic (pandas-dev#13488)

Author: Alex Alekseyev

doc/source/whatsnew/v0.21.0.txt

@@ -39,6 +39,8 @@ Other Enhancements
 - :func:`DataFrame.clip()` and :func: `Series.cip()` have gained an inplace argument. (:issue: `15388`)
 - :func:`crosstab` has gained a ``margins_name`` parameter to define the name of the row / column that will contain the totals when margins=True. (:issue:`15972`)
 - :func:`read_csv` has gained 'null' as an additional default missing value.(:issue:`16471`)
+- Frame arithmetic methods, such as :func:`DataFrame.add()`, now support ``fill_value`` even when the argument is a ``Series`` (:issue:`13488`)
+
 .. _whatsnew_0210.api_breaking:
 
 Backwards incompatible API changes

pandas/core/frame.py

@@ -3653,21 +3653,14 @@ def _combine_series_infer(self, other, func, level=None, fill_value=None):
 
     def _combine_match_index(self, other, func, level=None, fill_value=None):
         left, right = self.align(other, join='outer', axis=0, level=level,
-                                 copy=False)
-        if fill_value is not None:
-            raise NotImplementedError("fill_value %r not supported." %
-                                      fill_value)
+                                 copy=False, fill_value=fill_value)
         return self._constructor(func(left.values.T, right.values).T,
                                  index=left.index, columns=self.columns,
                                  copy=False)
 
     def _combine_match_columns(self, other, func, level=None, fill_value=None):
         left, right = self.align(other, join='outer', axis=1, level=level,
-                                 copy=False)
-        if fill_value is not None:
-            raise NotImplementedError("fill_value %r not supported" %
-                                      fill_value)
-
+                                 copy=False, fill_value=fill_value)
         new_data = left._data.eval(func=func, other=right,
                                    axes=[left.columns, self.index])
         return self._constructor(new_data)

pandas/tests/frame/test_operators.py

@@ -447,10 +447,26 @@ def test_arith_flex_frame(self):
 
         result = self.frame[:0].add(self.frame)
         assert_frame_equal(result, self.frame * np.nan)
-        with tm.assert_raises_regex(NotImplementedError, 'fill_value'):
-            self.frame.add(self.frame.iloc[0], fill_value=3)
-        with tm.assert_raises_regex(NotImplementedError, 'fill_value'):
-            self.frame.add(self.frame.iloc[0], axis='index', fill_value=3)
+
+    def test_arith_fill(self):
+        # GH 13488
+        df = DataFrame([[10.0, 11.0, 12.0, 13.0],
+                       [20.0, 21.0, 22.0, np.nan],
+                       [30.0, np.nan, np.nan, np.nan]])
+        s = Series([0.0, 1.0, 2.0, np.nan])
+
+        by_columns = DataFrame([[10.0, 12.0, 14.0, 13.0],
+                               [20.0, 22.0, 24.0, 0.0],
+                               [30.0, 1.0, 2.0, 0.0]])
+        assert_frame_equal(by_columns,
+                           df.add(s, fill_value=0.0))
+
+        by_index = DataFrame([[10.0, 11.0, 12.0, 13.0],
+                             [21.0, 22.0, 23.0, 1.0],
+                             [32.0, 2.0, 2.0, 2.0],
+                             [0.0, 0.0, 0.0, 0.0]])
+        assert_frame_equal(by_index,
+                           df.add(s, fill_value=0.0, axis='index'))
 
     def test_binary_ops_align(self):