NewBie question

Dear all,

I just joined this forum as a beginning Cocoa programmer. Nice to be here!I have been improving my programming skills on a little test project but at themoment I'm stuck. Hope you can help.

The situation:
I have an array filled with instances of the same class. This class keeps track of a process over time (I will not discuss this any further for now).The array is bound to a NSArrayController and in the UI a NSTableView is bound to the NSArrayController. The table view lists a number retrieved from every class instance in the array. This number reflects the state of the process that every class instance monitors.By default this numbers equals 0 what means that the process that is monitoredis not active.
At the moment all these class instances are displayed in the table even if the number in a given instance equals 0. 

I would like the following: 
- If the number equals 0 do not display that class instance in the table view
- If the number changes, reflect that change in the table viewHow do I accomplish this kind of feedback?   

Thanks.