Listbox limit possible selections based on another field
I'd like to be able to limit the available selections in a listbox based on a selection made on another specific chart. Using the function P (possible) doesn't work because as soon as a single selection is made in the listbox - the other possibilities go away. Sorting by frequency is also not as useful (even with show alternatives) as the list is very long. I'm not sure how I'd use set analysis for this - are there any suggestions?
I've attached a sample qvw to hopefully illustrate what I would like