DEPR: Change raw kwarg in rolling/expanding.apply to False

doc/source/whatsnew/v1.0.0.rst

@@ -414,6 +414,8 @@ or ``matplotlib.Axes.plot``. See :ref:`plotting.formatters` for more.
 - :func:`read_stata` and :meth:`DataFrame.to_stata` no longer supports the "encoding" argument (:issue:`21400`)
 - Removed previously deprecated "raise_conflict" argument from :meth:`DataFrame.update`, use "errors" instead (:issue:`23585`)
 - Removed previously deprecated keyword "n" from :meth:`DatetimeIndex.shift`, :meth:`TimedeltaIndex.shift`, :meth:`PeriodIndex.shift`, use "periods" instead (:issue:`22458`)
+- Changed the default value for the `raw` argument in :func:`Series.rolling().apply() <pandas.core.window.Rolling.apply>`, :func:`DataFrame.rolling().apply() <pandas.core.window.Rolling.apply>`,
+- :func:`Series.expanding().apply() <pandas.core.window.Expanding.apply>`, and :func:`DataFrame.expanding().apply() <pandas.core.window.Expanding.apply>` to ``False`` (:issue:`20584`)
 -
 
 .. _whatsnew_1000.performance:

pandas/core/window/expanding.py

@@ -148,7 +148,7 @@ def count(self, **kwargs):
 
     @Substitution(name="expanding")
     @Appender(_shared_docs["apply"])
-    def apply(self, func, raw=None, args=(), kwargs={}):
+    def apply(self, func, raw=False, args=(), kwargs={}):
         return super().apply(func, raw=raw, args=args, kwargs=kwargs)
 
     @Substitution(name="expanding")

pandas/core/window/rolling.py

@@ -6,7 +6,6 @@
 from functools import partial
 from textwrap import dedent
 from typing import Callable, Dict, List, Optional, Set, Tuple, Union
-import warnings
 
 import numpy as np
 
@@ -1190,15 +1189,11 @@ def count(self):
     raw : bool, default None
         * ``False`` : passes each row or column as a Series to the
           function.
-        * ``True`` or ``None`` : the passed function will receive ndarray
+        * ``True`` : the passed function will receive ndarray
           objects instead.
           If you are just applying a NumPy reduction function this will
           achieve much better performance.
 
-        The `raw` parameter is required and will show a FutureWarning if
-        not passed. In the future `raw` will default to False.
-
-        .. versionadded:: 0.23.0
     *args, **kwargs
         Arguments and keyword arguments to be passed into func.
 
@@ -1214,27 +1209,15 @@ def count(self):
     """
     )
 
-    def apply(self, func, raw=None, args=(), kwargs={}):
+    def apply(self, func, raw=False, args=(), kwargs={}):
         from pandas import Series
 
         kwargs.pop("_level", None)
         kwargs.pop("floor", None)
         window = self._get_window()
         offset = _offset(window, self.center)
-
-        # TODO: default is for backward compat
-        # change to False in the future
-        if raw is None:
-            warnings.warn(
-                "Currently, 'apply' passes the values as ndarrays to the "
-                "applied function. In the future, this will change to passing "
-                "it as Series objects. You need to specify 'raw=True' to keep "
-                "the current behaviour, and you can pass 'raw=False' to "
-                "silence this warning",
-                FutureWarning,
-                stacklevel=3,
-            )
-            raw = True
+        if not is_bool(raw):
+            raise ValueError("raw parameter must be `True` or `False`")
 
         window_func = partial(
             self._get_cython_func_type("roll_generic"),
@@ -1898,7 +1881,7 @@ def count(self):
 
     @Substitution(name="rolling")
     @Appender(_shared_docs["apply"])
-    def apply(self, func, raw=None, args=(), kwargs={}):
+    def apply(self, func, raw=False, args=(), kwargs={}):
         return super().apply(func, raw=raw, args=args, kwargs=kwargs)
 
     @Substitution(name="rolling")

pandas/tests/window/test_moments.py

@@ -687,17 +687,10 @@ def f(x):
         result = s.rolling(2, min_periods=0).apply(len, raw=raw)
         tm.assert_series_equal(result, expected)
 
-    @pytest.mark.parametrize("klass", [Series, DataFrame])
-    @pytest.mark.parametrize(
-        "method", [lambda x: x.rolling(window=2), lambda x: x.expanding()]
-    )
-    def test_apply_future_warning(self, klass, method):
-
-        # gh-5071
-        s = klass(np.arange(3))
-
-        with tm.assert_produces_warning(FutureWarning):
-            method(s).apply(lambda x: len(x))
+    @pytest.mark.parametrize("bad_raw", [None, 1, 0])
+    def test_rolling_apply_invalid_raw(self, bad_raw):
+        with pytest.raises(ValueError, match="raw parameter must be `True` or `False`"):
+            Series(range(3)).rolling(1).apply(len, raw=bad_raw)
 
     def test_rolling_apply_out_of_bounds(self, raw):
         # gh-1850