from Hacker News

Ask HN: algorithm used in Hacker News, that determines the front page news

by coderhs on 11/24/12, 6:19 AM with 4 comments

• by zio99 on 11/24/12, 6:35 AM

  Gravity.

  Score decreases over time, so interesting news bubble up, and older/no-longer-relevant news gradually decline.

      (= gravity* 1.8 timebase* 120 front-threshold* 1
         nourl-factor* .4 lightweight-factor* .17 gag-factor* .1)
  
      (def frontpage-rank (s (o scorefn realscore) (o gravity gravity*))
        (* (/ (let base (- (scorefn s) 1)
                (if (> base 0) (expt base .8) base))
              (expt (/ (+ (item-age s) timebase*) 60) gravity))
           (if (no (in s!type 'story 'poll))  .8
               (blank s!url)                  nourl-factor*
               (mem 'bury s!keys)             .001
                                              (* (contro-factor s)
                                                 (if (mem 'gag s!keys)
                                                      gag-factor*
                                                     (lightweight s)
                                                      lightweight-factor*
                                                     1)))))

• by pizza on 11/24/12, 6:41 AM

  direct copy from http://news.ycombinator.com/item?id=4746566

  According to the link in dmgrow's comment, it's

      Score = (P-1) / (T+2)^G
  

  where P is the number of votes, T is the time in hours since submission, and G is a power that controls the steepness/rate of decline in ranking, so popularity is decreases exponentially over time. I'm sure that YC-affiliated posts have a different ranking algorithm, considering you can't vote on them.

  Some other cool algorithms are:

  del.icio.us / delicious.com 's: ranked by upvotes in the last hour. I like the elegance of this solution a lot :)

  reddit's "best" feature: compares the rates at which comments are upvoted to generate the probability that a comment is a good one, which is how posts with fewer votes can be ranked better than posts with more votes. It works well, in my opinion.

• by bravoyankee on 11/24/12, 9:13 AM

  I think there's more to it than what the other two comments described. No doubt there is human moderation on HN (beyond users flagging submissions I mean), and maybe a list of domains and keywords to keep some stories from ever hitting front page, even when the submission gets a lot of votes in a short amount of time.

  Who knows what the reasons why they'd keep a story off the front page. The moderation is emo at times, even resorting to hellbanning, slowbanning etc.

  Slashdot moderation is way better. It's a better overall system over there.