Only viewing reply data by OP?

Hi, I have forum data based on different threads. Each entry is a post, and an id attaches seperate posts together to identify a thread. I want to be able to make a chart/graph, but only using data submitted by the original poster. For example, display the initial thread post, and then all follow up replies by the same user, discarding the rest. How can I accomplish this? I can filter graphs, but only if I manually select the user name. I would like to do it automatically. Thanks!