restrict lov depend on another partial lov

if i define 2 value setsbuild_vs 10 soap

              20 plastic

room_vs 1001 room1

               1002 room2

                2001 section1

i want when add asset when select build_vs 10 the lov of room_vs appears only room1 and room2(because i select 10 but in room_vs i substr the first 2 digits and appear the other digits)