Detect trend and sort by it

Hi, I have a report based on sentiment analysis. The data looks like this:

Each row is a post in a forum thread. Each post has an id that connects the posts as a thread. What I want to do is be able to detect the overall trend. Where does it start, and where does it end. This thread goes from negative to positive. (say 1 for positive trend, 0 for negative) But it would be nice to have a trend line equation. How can I take trend line data and sort threads by the trend (priotitize more negatively trending)? Thanks!