def transform(self, arg, *args, **kwargs):
return self._selected_obj.groupby(self.groupby).transform(<EOL>arg, *args, **kwargs)<EOL>
Call function producing a like-indexed Series on each group and return
a Series with the transformed values.

Parameters
----------
arg : function
    To apply to each group. Should return a Series with the same index.

Returns
-------
transformed : Series

Examples
--------
>>> resampled.transform(lambda x: (x - x.mean()) / x.std())