def grouped_filter(self):
return self.__class__.objects.all()<EOL>
This method should be overridden in order to allow groupings of
        ``RankModel`` objects.  The default is there is a single group which
        are all instances of the inheriting class.  

        An example with a grouped model would be::

            class Grouped(RankedModel):
                group_number = models.IntegerField()

                def grouped_filter(self):
                    return Grouped.objects.filter(
                        group_number=self.group_number)

        :returns:
            :class:`QuerySet` of ``RankedModel`` objects that are in the same
            group.