DOC: update the pandas.DataFrame.apply docstring

Author: mdeboc

pandas/core/frame.py

@@ -4859,18 +4859,18 @@ def apply(self, func, axis=0, broadcast=None, raw=False, reduce=None,
               achieve much better performance.
         reduce : bool or `None`, default `None`
             Try to apply reduction procedures. If the `DataFrame` is empty,
-            :meth:`apply` will use reduce to determine whether the result
+            :meth:`apply` will use `reduce` to determine whether the result
             should be a Series or a `DataFrame`. If ``reduce is None`` (the
             default), :meth:`apply`'s return value will be guessed by calling
-            func on an empty Series
+            `func` on an empty Series
             (note: while guessing, exceptions raised by `func` will be
             ignored).
-            If reduce is True a Series will always be returned, and if
-            `False` a `DataFrame` will always be returned.
+            If ``reduce is True`` a Series will always be returned, and if
+            ``reduce is False`` a `DataFrame` will always be returned.
 
             .. deprecated:: 0.23.0.
                This argument will be removed in a future version, replaced
-               by result_type='reduce'.
+               by ``result_type='reduce'``.
 
         result_type : {'expand', 'reduce', 'broadcast', `None`}
             These only act when ``axis=1`` (columns):
@@ -4898,9 +4898,9 @@ def apply(self, func, axis=0, broadcast=None, raw=False, reduce=None,
 
         Notes
         -----
-        In the current implementation apply calls func twice on the
+        In the current implementation apply calls `func` twice on the
         first column/row to decide whether it can take a fast or slow
-        code path. This can lead to unexpected behavior if func has
+        code path. This can lead to unexpected behavior if `func` has
         side-effects, as they will take effect twice for the first
         column/row.