Request: simple story promotion algorithm | Hacker News Reader

Request: simple story promotion algorithm

4 pointszemaj10 comments

Hi all,

I recently added a karma-like voting system to posts in a phpBB forum that was having some problems with spam (we have an point incentive system that users use to bid for real items - now instead of rewarding points for posts, they're now awarded for votes).

My question is; does anyone know a simple algorithm that can get a list of the "best-recent" posts based on votes. So simply if an item has a certain number of positive and negative points with each vote point made at a certain time, how can I combine that to get a list of highly voted, recent posts.

I could obviously research and come up with something myself, but there's probably quite a few people here who have experience in this area, so I thought it was worth a post!

Thanks, James

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PG recently posted the algorithm that news.yc uses:

http://news.ycombinator.com/item?id=38704

I use an algorithm where recent votes and posts has more weight:

(votes from the last two hours times 1) + (votes from the next two hours times 0.75)... and so on. Do the same for posts. Because it's expensive to calulate these values, I have a cron job that updates the scores every fifteen minutes.

Sounds perfect - thanks.

Presumably after several hours you could discount the votes altogether since they would have such a little influence on the final result. That would stop the system getting bogged down over time.

Out of interest, what is your "and so on". Do you go to 0.5 for the next 2 hours?

Yes, the so on means go to 0.5 for the next 2 hours. Of course you have to tweak the parameters to get the desired results for your site. It how all depends on how much you value recent posts and votes, versus overall votes. I also subtract a value depending on how old the post is. The site I use this for doesn't have any users, but it seems to work well in my limited testing.

Rank = ( ( current_time - post_time ) / number_of_votes )

Simple enough!

That would make everything start out at #1.

Presumably the "best" post would be the one with the lowest rank.

Yes. By the above formula, everything would have a rank of zero when it was first posted.

If you exclude everything with 0 votes, since you can't divide by 0 anyway, it might work.

Rank = ( ( current_time - post_time ) / number_of_votes ) ... considering number_of_votes is not equal to zero, Or better:

Rank = ( number_of_votes / ( current_time - post_time ) )

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