    def format_grouped_date(self, data, group):
        date = self.get_grouped_date(data, group)

        if group == 'week':
            date = u'%s — %s' % (
                (date - datetime.timedelta(days=6)).strftime('%d.%m'),
                date.strftime('%d.%m')
            )
        elif group == 'month':
            date = date.strftime('%b, %Y')
        else:
            date = formats.date_format(date, 'DATE_FORMAT')
        return date