Is it hot or not? Ranking of user modded content.

[ivankirigin]

Reddit and News.YC share a feature: hotness. Users mod up and down -- but hotness is more than total points.

How should I do it?

Positive correlation with number of votes. Negative correlation with submit time. Perhaps negative correlation with time since mean or median time of mods. Perhaps adjust for rates -- a surge implies extra hotness.

How do you make the front page efficiently? I hope not to recalculate hotness for each page view -- but a naive approach might think it necessary given the continuous time decay.

A parallel service could periodically troll through the entries from the past N days and calculate their hotness -- which serves the front page. That could be updated and chached in memory inependent of front pageview count.

[pg]

The way I do it is points divided by age in hours (plus two) to the 1.25th power. This is probably not optimal, but it's simple.

 (= gravity* 1.25 timebase* 120)

 (def hotness (s (o gravity gravity*))
   (/ (- (realscore s) 1)
      (expt (/ (+ (story-age s) timebase*) 60) gravity)))

I avoid reranking all the stories by keeping them in sorted order, and whenever I generate a frontpage for someone logged in, reinserting one randomly chosen story near the top (where all the change is). I also reinsert any story that gets voted on.

[run4yourlives → pg]

Thanks for sharing that Paul. Most people guard that knowledge like it's the lost grail.

Kudo to you for being open about it.

[ivankirigin → run4yourlives]

Indeed

[ivankirigin → pg]

Interesting. Right now, I have no data, making testing difficult -- especially for anything that will change hotness depending on distribution of mods in a given time.

It's been something I've been thinking about for a bit, and want to get it out of my head to focus on building something that people use so I can actually get the data.

[darragjm → ivankirigin]

Why not just start with a simple hotness algorithm and evolve it after data starts coming in?

[ivankirigin → darragjm]

That's exactly what I'll do.

[palish]

Speaking of karma, I wrote a little micro-essay about it at http://news.ycombinator.com/item?id=38605 .. I don't know if you'd want to experiment with karma quite like that, but it would be interesting.