@select_map(m:map, f:funct)
build a new map containing the entries of m which satisfy predicate f. This predicate takes two arguments: the key and the value. For instance 
       @fun_def pred($key, $value) { return ($key > "b") && ($value < 4) }
       $m := MAP{ ("a", 1), ("b", 2), ("c", 3), ("d", 4) }
       $mm := @select_map($m, @pred)
       print $mm
displays MAP{ ("c", 3) }

See also Map (aka dictionnary) @add_pair    @clear    [@clone]    @count    @domain    @find    @gshift_map    @insert    @is_defined    @is_function    @is_map    @listify    @make_duration_map    @make_label_bpm    @make_label_duration    @make_label_pitches    @make_label_pos    @make_score_map    @map    @map_compose    @map_concat    @map_history    @map_history_date    @map_history_rdate    @map_normalize    @map_reverse    @mapval    @max_key    @max_val    @member    @merge    @min_key    @min_val    @occurs    @range    @remove    @select_map    @shift_map