'Returns the list of field names the partner can be grouped (as merge
criteria) according to the option checked on the wizard'

@api.model
def _compute_selected_groupby(self):

    groups = []
    group_by_prefix = 'group_by_'
    for field_name in self._fields:
        if field_name.startswith(group_by_prefix):
            if getattr(self, field_name, False):
                groups.append(field_name[len(group_by_prefix):])
    if (not groups):
        raise UserError(_('You    have    to    specify    a    filter    for    your    selection'))
    return groups
