c# - Popularity decay algorithm for popular website posts -


i'm looking algorithm sort website results popularity.. reddit's older post less power it's votes/score has.

here accepted solution used reddit:

t = (time of entry post) - (dec 8, 2005) x = upvotes - downvotes  y = {1 if x > 0, 0 if x = 0, -1 if x < 0) z = {1 if x < 1, otherwise x}  rank = log(z) + (y * t)/45000

i've been on reddit's algorithm , although fit 1 situation, need 2 algorithms, 1 popular posts , upcoming posts:

  • popular posts
  • upcoming posts

popular decay slower, giving more weight older posts upcoming posts focus more on popular posts today, dropping off sharply after n hours/days/etc.

i'm writing using sphinx expressions can't write hugly complicated algo , have access following functions:

http://sphinxsearch.com/docs/current.html#numeric-functions

so have following data per post:

  • post age in seconds
  • post score

here current solution:

exponent = 0.01 (popular), 0.5 (upcoming) secondssincepublised = abs(curtimeinsecondssincedate-pubtimeinsecondssincedate) rank = (log10(postscore)*10000) / pow(secondssincepublised,exponent)

although solution work not ideal. new , popular post in last couple of hours ranks high in both popular , upcoming not want.

can suggest algorithm can modify exponent component adjust decay?

have tried ranking algorithm used hacker news? simple implement.

score = (p-1) / (t+2)^g  where, p = points of item (and -1 negate submitters vote) t = time since submission (in hours) g = gravity, defaults 1.8 in news.arc

you can vary gravity adjust decay.

for more information refer how hacker news ranking algorithm works


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