DOC: fix PR02 errors in docstring for pandas.core.groupby.SeriesGroupBy.apply

ci/code_checks.sh

@@ -136,7 +136,6 @@ if [[ -z "$CHECK" || "$CHECK" == "docstrings" ]]; then
         pandas.Timedelta.resolution\
         pandas.Interval\
         pandas.Grouper\
-        pandas.core.groupby.SeriesGroupBy.apply\
         pandas.core.groupby.DataFrameGroupBy.nth\
         pandas.core.groupby.DataFrameGroupBy.rolling\
         pandas.core.groupby.SeriesGroupBy.nth\

pandas/core/groupby/generic.py

@@ -72,7 +72,6 @@
     GroupByPlot,
     _agg_template_frame,
     _agg_template_series,
-    _apply_docs,
     _transform_template,
 )
 from pandas.core.indexes.api import (
@@ -214,12 +213,113 @@ def _get_data_to_aggregate(
     """
     )
 
-    @Appender(
-        _apply_docs["template"].format(
-            input="series", examples=_apply_docs["series_examples"]
-        )
-    )
     def apply(self, func, *args, **kwargs) -> Series:
+        """
+        Apply function ``func`` group-wise and combine the results together.
+
+        The function passed to ``apply`` must take a series as its first
+        argument and return a DataFrame, Series or scalar. ``apply`` will
+        then take care of combining the results back together into a single
+        dataframe or series. ``apply`` is therefore a highly flexible
+        grouping method.
+
+        While ``apply`` is a very flexible method, its downside is that
+        using it can be quite a bit slower than using more specific methods
+        like ``agg`` or ``transform``. Pandas offers a wide range of method that will
+        be much faster than using ``apply`` for their specific purposes, so try to
+        use them before reaching for ``apply``.
+
+        Parameters
+        ----------
+        func : callable
+            A callable that takes a series as its first argument, and
+            returns a dataframe, a series or a scalar. In addition the
+            callable may take positional and keyword arguments.
+
+        *args : tuple
+            Optional positional arguments to pass to ``func``.
+
+        **kwargs : dict
+            Optional keyword arguments to pass to ``func``.
+
+        Returns
+        -------
+        Series or DataFrame
+
+        See Also
+        --------
+        pipe : Apply function to the full GroupBy object instead of to each
+            group.
+        aggregate : Apply aggregate function to the GroupBy object.
+        transform : Apply function column-by-column to the GroupBy object.
+        Series.apply : Apply a function to a Series.
+        DataFrame.apply : Apply a function to each row or column of a DataFrame.
+
+        Notes
+        -----
+
+        .. versionchanged:: 1.3.0
+
+            The resulting dtype will reflect the return value of the passed ``func``,
+            see the examples below.
+
+        Functions that mutate the passed object can produce unexpected
+        behavior or errors and are not supported. See :ref:`gotchas.udf-mutation`
+        for more details.
+
+        Examples
+        --------
+        >>> s = pd.Series([0, 1, 2], index='a a b'.split())
+        >>> g1 = s.groupby(s.index, group_keys=False)
+        >>> g2 = s.groupby(s.index, group_keys=True)
+
+        From ``s`` above we can see that ``g`` has two groups, ``a`` and ``b``.
+        Notice that ``g1`` have ``g2`` have two groups, ``a`` and ``b``, and only
+        differ in their ``group_keys`` argument. Calling `apply` in various ways,
+        we can get different grouping results:
+
+        Example 1: The function passed to `apply` takes a Series as
+        its argument and returns a Series.  `apply` combines the result for
+        each group together into a new Series.
+
+        .. versionchanged:: 1.3.0
+
+            The resulting dtype will reflect the return value of the passed ``func``.
+
+        >>> g1.apply(lambda x: x * 2 if x.name == 'a' else x / 2)
+        a    0.0
+        a    2.0
+        b    1.0
+        dtype: float64
+
+        In the above, the groups are not part of the index. We can have them included
+        by using ``g2`` where ``group_keys=True``:
+
+        >>> g2.apply(lambda x: x * 2 if x.name == 'a' else x / 2)
+        a  a    0.0
+           a    2.0
+        b  b    1.0
+        dtype: float64
+
+        Example 2: The function passed to `apply` takes a Series as
+        its argument and returns a scalar. `apply` combines the result for
+        each group together into a Series, including setting the index as
+        appropriate:
+
+        >>> g1.apply(lambda x: x.max() - x.min())
+        a    1
+        b    0
+        dtype: int64
+
+        The ``group_keys`` argument has no effect here because the result is not
+        like-indexed (i.e. :ref:`a transform <groupby.transform>`) when compared
+        to the input.
+
+        >>> g2.apply(lambda x: x.max() - x.min())
+        a    1
+        b    0
+        dtype: int64
+        """
         return super().apply(func, *args, **kwargs)
 
     @doc(_agg_template_series, examples=_agg_examples_doc, klass="Series")