EHN: Implement method argument for DataFrame.replace (pandas-dev#19894)

Author: reidy-p

doc/source/whatsnew/v0.23.0.txt

@@ -338,6 +338,7 @@ Other Enhancements
 - For subclassed ``DataFrames``, :func:`DataFrame.apply` will now preserve the ``Series`` subclass (if defined) when passing the data to the applied function (:issue:`19822`)
 - :func:`DataFrame.from_dict` now accepts a ``columns`` argument that can be used to specify the column names when ``orient='index'`` is used (:issue:`18529`)
 - Added option ``display.html.use_mathjax`` so `MathJax <https://www.mathjax.org/>`_ can be disabled when rendering tables in ``Jupyter`` notebooks (:issue:`19856`, :issue:`19824`)
+- :func:`DataFrame.replace` now supports the ``method`` parameter, which can be used to specify the replacement method when ``to_replace`` is a scalar, list or tuple and ``value`` is ``None`` (:issue:`19632`)
 - :meth:`Timestamp.month_name`, :meth:`DatetimeIndex.month_name`, and :meth:`Series.dt.month_name` are now available (:issue:`12805`)
 - :meth:`Timestamp.day_name` and :meth:`DatetimeIndex.day_name` are now available to return day names with a specified locale (:issue:`12806`)
 

pandas/core/generic.py

@@ -4886,7 +4886,10 @@ def bfill(self, axis=None, inplace=False, limit=None, downcast=None):
             ``to_replace`` must be ``None``.
         method : string, optional, {'pad', 'ffill', 'bfill'}
             The method to use when for replacement, when ``to_replace`` is a
-            ``list``.
+            scalar, list or tuple and ``value`` is None.
+
+        .. versionchanged:: 0.23.0
+           Added to DataFrame
 
         See Also
         --------
@@ -5055,6 +5058,10 @@ def replace(self, to_replace=None, value=None, inplace=False, limit=None,
                 to_replace = [to_replace]
 
             if isinstance(to_replace, (tuple, list)):
+                if isinstance(self, pd.DataFrame):
+                    return self.apply(_single_replace,
+                                      args=(to_replace, method, inplace,
+                                            limit))
                 return _single_replace(self, to_replace, method, inplace,
                                        limit)
 

pandas/tests/frame/test_replace.py

@@ -33,9 +33,6 @@ def test_replace_inplace(self):
         tsframe.replace(nan, 0, inplace=True)
         assert_frame_equal(tsframe, self.tsframe.fillna(0))
 
-        pytest.raises(TypeError, self.tsframe.replace, nan, inplace=True)
-        pytest.raises(TypeError, self.tsframe.replace, nan)
-
         # mixed type
         mf = self.mixed_frame
         mf.iloc[5:20, mf.columns.get_loc('foo')] = nan
@@ -720,7 +717,6 @@ def test_replace_simple_nested_dict_with_nonexistent_value(self):
         assert_frame_equal(expected, result)
 
     def test_replace_value_is_none(self):
-        pytest.raises(TypeError, self.tsframe.replace, nan)
         orig_value = self.tsframe.iloc[0, 0]
         orig2 = self.tsframe.iloc[1, 0]
 
@@ -1072,3 +1068,36 @@ def test_replace_with_empty_dictlike(self):
 
         assert_frame_equal(df, df.replace({'b': {}}))
         assert_frame_equal(df, df.replace(Series({'b': {}})))
+
+    @pytest.mark.parametrize("to_replace, method, expected", [
+        (0, 'bfill', {'A': [1, 1, 2],
+                      'B': [5, nan, 7],
+                      'C': ['a', 'b', 'c']}),
+        (nan, 'bfill', {'A': [0, 1, 2],
+                        'B': [5.0, 7.0, 7.0],
+                        'C': ['a', 'b', 'c']}),
+        ('d', 'ffill', {'A': [0, 1, 2],
+                        'B': [5, nan, 7],
+                        'C': ['a', 'b', 'c']}),
+        ([0, 2], 'bfill', {'A': [1, 1, 2],
+                           'B': [5, nan, 7],
+                           'C': ['a', 'b', 'c']}),
+        ([1, 2], 'pad', {'A': [0, 0, 0],
+                         'B': [5, nan, 7],
+                         'C': ['a', 'b', 'c']}),
+        ((1, 2), 'bfill', {'A': [0, 2, 2],
+                           'B': [5, nan, 7],
+                           'C': ['a', 'b', 'c']}),
+        (['b', 'c'], 'ffill', {'A': [0, 1, 2],
+                               'B': [5, nan, 7],
+                               'C': ['a', 'a', 'a']}),
+    ])
+    def test_replace_method(self, to_replace, method, expected):
+        # GH 19632
+        df = DataFrame({'A': [0, 1, 2],
+                        'B': [5, nan, 7],
+                        'C': ['a', 'b', 'c']})
+
+        result = df.replace(to_replace=to_replace, value=None, method=method)
+        expected = DataFrame(expected)
+        assert_frame_equal(result, expected)