blairanderson
10/25/2014 - 4:50 AM

Reddit Algorithm in Ruby - converted from https://github.com/reddit/reddit/blob/master/sql/functions.sql

Reddit Algorithm in Ruby - converted from https://github.com/reddit/reddit/blob/master/sql/functions.sql

functions.sql
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-- The contents of this file are subject to the Common Public Attribution
-- License Version 1.0. (the "License"); you may not use this file except in
-- compliance with the License. You may obtain a copy of the License at
-- http://code.reddit.com/LICENSE. The License is based on the Mozilla Public
-- License Version 1.1, but Sections 14 and 15 have been added to cover use of
-- software over a computer network and provide for limited attribution for the
-- Original Developer. In addition, Exhibit A has been modified to be
-- consistent with Exhibit B.
--
-- Software distributed under the License is distributed on an "AS IS" basis,
-- WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for
-- the specific language governing rights and limitations under the License.
--
-- The Original Code is reddit.
--
-- The Original Developer is the Initial Developer.  The Initial Developer of
-- the Original Code is reddit Inc.
--
-- All portions of the code written by reddit are Copyright (c) 2006-2014
-- reddit Inc. All Rights Reserved.
-------------------------------------------------------------------------------

create or replace function hot(ups integer, downs integer, date timestamp with time zone) returns numeric as $$
    select round(cast(log(greatest(abs($1 - $2), 1)) * sign($1 - $2) + (date_part('epoch', $3) - 1134028003) / 45000.0 as numeric), 7)
$$ language sql immutable;

create or replace function score(ups integer, downs integer) returns integer as $$
    select $1 - $2
$$ language sql immutable;

create or replace function controversy(ups integer, downs integer) returns float as $$
    select CASE WHEN $1 <= 0 or $2 <= 0 THEN 0
                WHEN $1 > $2 THEN power($1 + $2, cast($2 as float) / $1)
                ELSE power($1 + $2, cast($1 as float) / $2)
           END;
$$ language sql immutable;

create or replace function ip_network(ip text) returns text as $$
    select substring($1 from E'[\\d]+\.[\\d]+\.[\\d]+')
$$ language sql immutable;

create or replace function base_url(url text) returns text as $$
    select substring($1 from E'(?i)(?:.+?://)?(?:www[\\d]*\\.)?([^#]*[^#/])/?')
$$ language sql immutable;

create or replace function domain(url text) returns text as $$
    select substring($1 from E'(?i)(?:.+?://)?(?:www[\\d]*\\.)?([^#/]*)/?')
$$ language sql immutable;
reddit_hot_calculator.md
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  • Rendered
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The hot calculator is adapted from the actual reddit sql code defined in github: https://github.com/reddit/reddit/blob/master/sql/functions.sql

class RedditHotCalculator
  EPOCH = Time.local(1999, 1, 1, 1, 1, 1).to_time
  
  # date is a ruby Time
  def initialize(downs, ups, date)
    @ups = ups
    @downs = downs
    @date = date
  end

  def epoch_seconds
    (@date.to_i - EPOCH.to_i).to_f
  end

  def displacement
    Math.log([difference.abs, 1].max, 10)
  end

  def difference
    @ups - @downs
  end

  def sign
    return 1 if difference > 0
    return -1 if difference < 0
    return 0
  end

  def hot
    return ((displacement * sign.to_f) + (epoch_seconds / 45000))
  end

end

calc = RedditHotCalculator.new(10, 2, Date.now)
calc.hot