How to report only properties from a Listbox?

I have a listbox with a list of properties from a database and I want to be able to keep only the properties selected in the listbox.

I have tried so far without success:

1) keep(@property_List). This removes all properties.

2)

> Custom Manipulator

          1. Initial expression : expand(',',(@property_List)

          2. Expression: Keep(@property_List).

Thanks