ENH: Support inplace clip (pandas-dev#15388)

doc/source/whatsnew/v0.21.0.txt

@@ -36,6 +36,7 @@ Other Enhancements
 - :func:`to_pickle` has gained a protocol parameter (:issue:`16252`). By default, this parameter is set to `HIGHEST_PROTOCOL <https://docs.python.org/3/library/pickle.html#data-stream-format>`__
 - :func:`api.types.infer_dtype` now infers decimals. (:issue: `15690`)
 - :func:`read_feather` has gained the ``nthreads`` parameter for multi-threaded operations (:issue:`16359`)
+- :func:`DataFrame.clip()` and :func: `Series.cip()` have gained an inplace argument. (:issue: `15388`)
 
 .. _whatsnew_0210.api_breaking:
 

pandas/core/generic.py

@@ -4120,8 +4120,7 @@ def isnull(self):
     def notnull(self):
         return notnull(self).__finalize__(self)
 
-    def _clip_with_scalar(self, lower, upper):
-
+    def _clip_with_scalar(self, lower, upper, inplace=False):
         if ((lower is not None and np.any(isnull(lower))) or
                 (upper is not None and np.any(isnull(upper)))):
             raise ValueError("Cannot use an NA value as a clip threshold")
@@ -4137,10 +4136,16 @@ def _clip_with_scalar(self, lower, upper):
         if np.any(mask):
             result[mask] = np.nan
 
-        return self._constructor(
-            result, **self._construct_axes_dict()).__finalize__(self)
+        axes_dict = self._construct_axes_dict()
+        result = self._constructor(result, **axes_dict).__finalize__(self)
+
+        if inplace:
+            self._update_inplace(result)
+        else:
+            return result
 
-    def clip(self, lower=None, upper=None, axis=None, *args, **kwargs):
+    def clip(self, lower=None, upper=None, axis=None, inplace=False,
+             *args, **kwargs):
         """
         Trim values at input threshold(s).
 
@@ -4150,6 +4155,9 @@ def clip(self, lower=None, upper=None, axis=None, *args, **kwargs):
         upper : float or array_like, default None
         axis : int or string axis name, optional
             Align object with lower and upper along the given axis.
+        inplace : boolean, default False
+            Whether to perform the operation in place on the data
+                .. versionadded:: 0.21.0
 
         Returns
         -------
@@ -4192,6 +4200,8 @@ def clip(self, lower=None, upper=None, axis=None, *args, **kwargs):
         if isinstance(self, ABCPanel):
             raise NotImplementedError("clip is not supported yet for panels")
 
+        inplace = validate_bool_kwarg(inplace, 'inplace')
+
         axis = nv.validate_clip_with_axis(axis, args, kwargs)
 
         # GH 2747 (arguments were reversed)
@@ -4202,17 +4212,20 @@ def clip(self, lower=None, upper=None, axis=None, *args, **kwargs):
         # fast-path for scalars
         if ((lower is None or (is_scalar(lower) and is_number(lower))) and
                 (upper is None or (is_scalar(upper) and is_number(upper)))):
-            return self._clip_with_scalar(lower, upper)
+            return self._clip_with_scalar(lower, upper, inplace=inplace)
 
         result = self
         if lower is not None:
-            result = result.clip_lower(lower, axis)
+            result = result.clip_lower(lower, axis, inplace=inplace)
         if upper is not None:
-            result = result.clip_upper(upper, axis)
+            if inplace:
+                result = self
+
+            result = result.clip_upper(upper, axis, inplace=inplace)
 
         return result
 
-    def clip_upper(self, threshold, axis=None):
+    def clip_upper(self, threshold, axis=None, inplace=False):
         """
         Return copy of input with values above given value(s) truncated.
 
@@ -4221,6 +4234,9 @@ def clip_upper(self, threshold, axis=None):
         threshold : float or array_like
         axis : int or string axis name, optional
             Align object with threshold along the given axis.
+        inplace : boolean, default False
+            Whether to perform the operation in place on the data
+                .. versionadded:: 0.21.0
 
         See Also
         --------
@@ -4234,12 +4250,14 @@ def clip_upper(self, threshold, axis=None):
             raise ValueError("Cannot use an NA value as a clip threshold")
 
         if is_scalar(threshold) and is_number(threshold):
-            return self._clip_with_scalar(None, threshold)
+            return self._clip_with_scalar(None, threshold, inplace=inplace)
+
+        inplace = validate_bool_kwarg(inplace, 'inplace')
 
         subset = self.le(threshold, axis=axis) | isnull(self)
-        return self.where(subset, threshold, axis=axis)
+        return self.where(subset, threshold, axis=axis, inplace=inplace)
 
-    def clip_lower(self, threshold, axis=None):
+    def clip_lower(self, threshold, axis=None, inplace=False):
         """
         Return copy of the input with values below given value(s) truncated.
 
@@ -4248,6 +4266,9 @@ def clip_lower(self, threshold, axis=None):
         threshold : float or array_like
         axis : int or string axis name, optional
             Align object with threshold along the given axis.
+        inplace : boolean, default False
+            Whether to perform the operation in place on the data
+                .. versionadded:: 0.21.0
 
         See Also
         --------
@@ -4261,10 +4282,12 @@ def clip_lower(self, threshold, axis=None):
             raise ValueError("Cannot use an NA value as a clip threshold")
 
         if is_scalar(threshold) and is_number(threshold):
-            return self._clip_with_scalar(threshold, None)
+            return self._clip_with_scalar(threshold, None, inplace=inplace)
+
+        inplace = validate_bool_kwarg(inplace, 'inplace')
 
         subset = self.ge(threshold, axis=axis) | isnull(self)
-        return self.where(subset, threshold, axis=axis)
+        return self.where(subset, threshold, axis=axis, inplace=inplace)
 
     def groupby(self, by=None, axis=0, level=None, as_index=True, sort=True,
                 group_keys=True, squeeze=False, **kwargs):

pandas/tests/frame/test_analytics.py

@@ -1807,6 +1807,7 @@ def test_built_in_round(self):
 
     def test_clip(self):
         median = self.frame.median().median()
+        original = self.frame.copy()
 
         capped = self.frame.clip_upper(median)
         assert not (capped.values > median).any()
@@ -1817,6 +1818,25 @@ def test_clip(self):
         double = self.frame.clip(upper=median, lower=median)
         assert not (double.values != median).any()
 
+        # Verify that self.frame was not changed inplace
+        assert (self.frame.values == original.values).all()
+
+    def test_inplace_clip(self):
+        # GH #15388
+        median = self.frame.median().median()
+        frame_copy = self.frame.copy()
+
+        frame_copy.clip_upper(median, inplace=True)
+        assert not (frame_copy.values > median).any()
+        frame_copy = self.frame.copy()
+
+        frame_copy.clip_lower(median, inplace=True)
+        assert not (frame_copy.values < median).any()
+        frame_copy = self.frame.copy()
+
+        frame_copy.clip(upper=median, lower=median, inplace=True)
+        assert not (frame_copy.values != median).any()
+
     def test_dataframe_clip(self):
         # GH #2747
         df = DataFrame(np.random.randn(1000, 2))
@@ -1843,18 +1863,23 @@ def test_clip_mixed_numeric(self):
                               'B': [1., np.nan, 2.]})
         tm.assert_frame_equal(result, expected, check_like=True)
 
-    def test_clip_against_series(self):
+    @pytest.mark.parametrize("inplace", [True, False])
+    def test_clip_against_series(self, inplace):
         # GH #6966
 
         df = DataFrame(np.random.randn(1000, 2))
         lb = Series(np.random.randn(1000))
         ub = lb + 1
 
-        clipped_df = df.clip(lb, ub, axis=0)
+        original = df.copy()
+        clipped_df = df.clip(lb, ub, axis=0, inplace=inplace)
+
+        if inplace:
+            clipped_df = df
 
         for i in range(2):
-            lb_mask = df.iloc[:, i] <= lb
-            ub_mask = df.iloc[:, i] >= ub
+            lb_mask = original.iloc[:, i] <= lb
+            ub_mask = original.iloc[:, i] >= ub
             mask = ~lb_mask & ~ub_mask
 
             result = clipped_df.loc[lb_mask, i]