How to iterate on form array member in c# server (client is Extjs form)

In the server I get my arrays as such string: 0:val1,1:val2,2:val3

I work with NameValueCollection but this iterates through all the form members. How do I parse\iterate through array form member to get a neat array of {"val1","val2","val3"} without its index?

BTW - the client was sent with ExtJs Form submit...(maybe its something in the client?)