

Reddit, Stumbleupon, Del.icio.us and Hacker News Algorithms Exposed - marrone
http://www.seomoz.org/blog/reddit-stumbleupon-delicious-and-hacker-news-algorithms-exposed

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babul
These are not the algorithms but an overview of the formulas.

For example the HN algorithm is outlined in several places e.g.
<http://news.ycombinator.com/item?id=38704> and on the pg Arc site, and the
reddit algorithms is

    
    
      def hot(ups, downs, date):
      s = score(ups, downs)
      order = log(max(abs(s), 1), 10)
      sign = 1 if s > 0 else -1 if s < 0 else 0
      seconds = epoch_seconds(date) - 1134028003
      return round(order + sign * seconds / 45000, 7)

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joshu
the delicious one is wrong.

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DannyDover
Thanks for reading the post. What do you think is wrong with the del.icio.us
formula?

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aston
You just demonstrated one of the coolest things about posting at news.yc. You
never know who you're gonna run into. Even when they're replying directly to
you.

edit: Hint, click his name...

~~~
joshu
:)

~~~
markbao
This is why I love Hacker News.

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gojomo
Use of true clock time in these formulas penalizes posts that are submitted at
low-traffic times.

Using a virtual clock, such as a tick count based on traffic (number of other
submissions, votes, pageviews, etc.), could adjust for this.

~~~
brent
Good observation. I believe a similar concept is used in high frequency
trading (in markets such as foreign exchange). So derivatives are not dt, but
du where u is a surrogate for time in ticks.

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pierrefar
For reddit, this is the public algo released with their code. I think we
should not assume that's the algo they use on reddit.com. Think about it: they
could easily release a basic algo and keep the good one for their own internal
use.

At the very least, even reddit's blog post announcement of the code mentioned
they're not open sourcing the spam detection code. Surely that's part of the
ranking algo in that it determines if a submission gets ranked or not.

For the SU one, I think there is more to the story, but that's for another
post...

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pg
I don't think they'd bother trying to fake people out by releasing a different
ranking algorithm than they used on the site. There wouldn't be any point
anyway. Knowing how to get onto the frontpage of a venetian-blind site like
Digg might be useful to spammers, but knowing the ranking algorithm of a
bubble-up site like Reddit or News.YC wouldn't help them much.

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globalrev
Not to be an ass but how hard can they be anyway? Its not a formula like a^2 +
b^2 = c^2

it is just some variables that they tweaked until they fit.

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lakeeffect
I thought karma had an influence on how something appears. If not what is the
point of karma?

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schtog
To keep you in line unfortuneately.

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Jax
Yippee! Thats great. But how did u findout delicious's and stumbleupon's? By
reverse engineering technique... like... Were these found out(or guess-worked)
by constantly keeping track of the ranking of content?

Joshu, i think the del.icio.us formula is right, or they might just be using a
different time constraint than 1 hour(maybe 2hrs or anything else). Because to
findout what's popular they dont require any complex stuff. Simple math as
specified in Danny's post is enough for their task.

Go Danny! Go!!!

~~~
gojomo
I would trust user 'joshu' on matters related to del.icio.us.

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Jax
God!

Gojomo, is that really Joshua, the founder of Delicious and Memepool? I just
guessed it when u mentioned the username in single quotes. ;) I wouldn't talk
a word abt the algo then. :D

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iamelgringo
click on 'joshu' 's user name.

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byrneseyeview
It would be nice to have a less misleading title. I clicked to find out what
Digg's algorithm is.

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randfish
Wait - the title doesn't include Digg, so how exactly is it misleading? Maybe
you're being sarcastic and my sarcasm detector just isn't well-tuned.

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byrneseyeview
The title was edited, apparently. When I clicked, it said Digg, and the
article still has a section on Digg.

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redorb
can't be to hard to finds .yc's - cause its open. i hope this doesn't send a
flood of seo's ;)

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Raphael
Mathematically speaking, would it make a difference to use p^2 / t instead of
p / t^2?

