def get_and_group_by_field(cr, uid, obj, ids, field, context=None):
    """ Read the values of ``field´´ for the given ``ids´´ and group ids by value.

       :param string field: name of the field we want to read and group by
       :return: mapping of field values to the list of ids that have it
       :rtype: dict
    """
    res = {}
    for record in obj.read(cr, uid, ids, [field], context=context):
        key = record[field]
        res.setdefault(key[0] if isinstance(key, tuple) else key, []).append(record['id'])
    return res