ENH: can pass dict of values per column to DataFrame.fillna, close #661

pandas/core/frame.py

@@ -2402,8 +2402,10 @@ def fillna(self, value=None, method='pad', inplace=False):
             Method to use for filling holes in reindexed Series
             pad / ffill: propagate last valid observation forward to next valid
             backfill / bfill: use NEXT valid observation to fill gap
-        value : any kind (should be same type as array)
-            Value to use to fill holes (e.g. 0)
+        value : scalar or dict
+            Value to use to fill holes (e.g. 0), alternately a dict of values
+            specifying which value to use for each column (columns not in the
+            dict will not be filled)
         inplace : boolean, default False
             If True, fill the DataFrame in place. Note: this will modify any
             other views on this DataFrame, like if you took a no-copy slice of
@@ -2438,7 +2440,17 @@ def fillna(self, value=None, method='pad', inplace=False):
             # Float type values
             if len(self.columns) == 0:
                 return self
-            new_data = self._data.fillna(value)
+            if np.isscalar(value):
+                new_data = self._data.fillna(value, inplace=inplace)
+            elif isinstance(value, dict):
+                result = self if inplace else self.copy()
+                for k, v in value.iteritems():
+                    if k not in result:
+                        continue
+                    result[k].fillna(v, inplace=True)
+                return result
+            else:  # pragma: no cover
+                raise TypeError('Invalid fill value type: %s' % type(value))
 
         if inplace:
             self._data = new_data

pandas/core/internals.py

@@ -201,15 +201,20 @@ def split_block_at(self, item):
             left_block = make_block(self.values[:loc],
                                     self.items[:loc].copy(), self.ref_items)
             right_block = make_block(self.values[loc + 1:],
-                                     self.items[loc + 1:].copy(), self.ref_items)
+                                     self.items[loc + 1:].copy(),
+                                     self.ref_items)
 
         return left_block, right_block
 
-    def fillna(self, value):
-        new_values = self.values.copy()
+    def fillna(self, value, inplace=False):
+        new_values = self.values if inplace else self.values.copy()
         mask = com.isnull(new_values.ravel())
         new_values.flat[mask] = value
-        return make_block(new_values, self.items, self.ref_items)
+
+        if inplace:
+            return self
+        else:
+            return make_block(new_values, self.items, self.ref_items)
 
     def interpolate(self, method='pad', inplace=False):
         values = self.values if inplace else self.values.copy()
@@ -931,11 +936,14 @@ def add_suffix(self, suffix):
         f = ('%s' + ('%s' % suffix)).__mod__
         return self.rename_items(f)
 
-    def fillna(self, value):
+    def fillna(self, value, inplace=False):
         """
 
         """
-        new_blocks = [b.fillna(value) for b in self.blocks]
+        new_blocks = [b.fillna(value, inplace=inplace)
+                      for b in self.blocks]
+        if inplace:
+            return self
         return BlockManager(new_blocks, self.axes)
 
     @property

pandas/tests/test_frame.py

@@ -2968,6 +2968,21 @@ def test_fillna_inplace(self):
         self.assert_(df2 is df)
         assert_frame_equal(df2, expected)
 
+    def test_fillna_dict(self):
+        df = DataFrame({'a': [nan, 1, 2, nan, nan],
+                        'b': [1, 2, 3, nan, nan],
+                        'c': [nan, 1, 2, 3, 4]})
+
+        result = df.fillna({'a': 0, 'b': 5})
+
+        expected = df.copy()
+        expected['a'] = expected['a'].fillna(0)
+        expected['b'] = expected['b'].fillna(5)
+        assert_frame_equal(result, expected)
+
+        # it works
+        result = df.fillna({'a': 0, 'b': 5, 'd' : 7})
+
     def test_truncate(self):
         offset = datetools.bday
 

vb_suite/frame_methods.py

@@ -23,3 +23,13 @@
 frame_fancy_lookup_all = Benchmark('df.lookup(row_labels_all, col_labels_all)',
                                    setup,
                                    start_date=datetime(2012, 1, 12))
+
+#----------------------------------------------------------------------
+# fillna in place
+
+setup = common_setup + """
+df = DataFrame(randn(10000, 100))
+df.values[::2] = np.nan
+"""
+
+frame_fillna_inplace = Benchmark('df.fillna(0, inplace=True)', setup)