@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) }