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reddit 'hot' algorithm, in ruby, with typo fixed
require 'date'
# Actually doesn't matter WHAT you choose as the epoch, it
# won't change the algorithm. Just don't change it after you
# have cached computed scores. Choose something before your first
# post to avoid annoying negative numbers. Choose something close
# to your first post to keep the numbers smaller. This is, I think,
# reddit's own epoch.
$our_epoch = Time.local(2005, 12, 8, 7, 46, 43).to_time
def epoch_seconds(t)
(t.to_i - $our_epoch.to_i).to_f
# date is a ruby Time
def hot(ups, downs, date)
s = ups - downs
displacement = Math.log( [s.abs, 1].max, 10 )
sign = if s > 0
elsif s < 0
return (displacement * sign.to_f) + ( epoch_seconds(date) / 45000 )

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