Creating a concatenate text list by referencing an array
 

I need help creating a formula to create a concatenated list from a matrix by
referencing a second array.

Spread sheet layout: Data

Programs (A:5) Line (B:5)
product 1 1
product 2 2
product 3 1
product 4 1 (B:9)

Starting in Cell A:11 would be the concatenate formula for the Programs,
B:11 would be the Line # (array), starting with 1 and going to 6 (B:17). The
formula criteria would be B:11 thru B:17. So for Line #1 (B:11), A:11 should
show "product 1, product 3, product 4". A:12 would be the formula for Line
#2 showing "product 2". Let me know if you need more info.