The Reddit Algorithm

Tim Wintle - July 4th, 2008

As a developer working on the Viral Ad Network (our advertainment network), and viral video search engine viral sauce (and with a recent MSci in Maths – so excuse the equations), I’ve worked on a fair share of social media ranking algorithms, so I found this discovery of the algorithms behind some of the top social sites very interesting. These are well sourced, and very informative to anyone in the middle of a viral seeding campaign. Here is a perfect example:
Reddit:
let

t = (t1 – epoch)

(where t1 is the time the post was made)

let x be the number of up votes minus the number of down votes.

Then,

let y be:

  • 1 if there are more up votes than down votes,
  • -1 If there are more down voets than up votes,
  • 0 if there are the same number.

Now Let

z = max({x,1})

And We Have

ranking = C log10(z) + yt1

Where C is a constant (C = 45000).

You can find more algorithms in this great article.

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