def remove_invalid_fields(self, queryset, fields, view):
        valid_orderings = []
        invalid_orderings = []
        for term in fields:
            stripped_term = term.lstrip('-')
            reverse_sort_term = '' if len(stripped_term) is len(term) else '-'
            ordering = self.ordering_for(stripped_term, view)
            if ordering:
                valid_orderings.append(reverse_sort_term + ordering)
            else:
                invalid_orderings.append(term)
        return valid_orderings, invalid_orderings