CODEWITHSUNDEEP
phpmysqlalgorithmrankingreddit
user3614800
user3614800

Reputation: 73

PHP Reddit Ranking Algorithm - Calculate Rank

I'm working on a discussion board, which is listing all topics according on it's hotness/rank (like reddit). So i took reddits algorithm and started trying. i used this example: http://blog.sodhanalibrary.com/2014/04/reddit-ranking-algorithm-implementation.html

function score($ups,$downs){
    return $ups - $downs;
}

function epoch_seconds($timestamp){
    $epoch = new DateTime("1970-01-01 00:00:00");
    $unix = new DateTime($timestamp);
    $td = $epoch->diff($unix);

    $days = $td->format('%a');
    $hours = $td->format('%h');
    $minutes = $td->format('%i');
    $seconds = $td->format('%s');
    $age = ($days * 86400) + ($hours * 3600) + ($minutes * 60) + $seconds;

    return $age;
}

function calculateRank($ups,$downs,$date){
    $s = score($ups,$downs);
    $order = log10(max(abs($s), 1), 10); 

    if($s > 0) {
        $sign = 1;
    } elseif($s < 0) {
        $sign = -1;
    } else {
        $sign = 0;
    }

    $seconds = epoch_seconds($date) - 1134028003;

    return round($order + (($sign * $seconds)/45000), 7);
}

Example:

echo calculateRank(1,0,"2015-02-14 12:00:00"); // = 6441.9377111

What i do not understand, is the fact, that if the score (the difference between upvotes and downvotes) is 0, then the rank is 0. This would mean, that a completely new article with +1/-1 would be ranked in nirvana.

echo calculateRank(1,1,"2015-02-14 12:00:00"); // = 0

Also, if the score is negative the rank is negative. Which means that a completely new article with a +1/-2 would be ranked even further away then nirvana.

echo calculateRank(1,2,"2015-02-14 12:00:00"); // = -6441.9377111

The Select Query would look something like this:

SELECT * FROM articles ORDER BY rank DESC

According to the results i showed you, that would mean that an 10 year old article with a positive score (eg: 1 upvote / 0 downvotes), would be ranked higher, then EVERY article with a score of 0 or a negative score, no matter of the date. That cannot be right and confuses me.

What i'm looking for is something similar. I already got rid of zero-ranks by do not allowing a score of 0. However, negative scores (eg: 0 upvotes / 2 downvotes) should lower the score instead of inverting it.

Any help is highly appreciated! Thanks.

Upvotes: 0

Views: 1721

Answers (1)

user3614800
user3614800

Reputation: 73

I adjusted the algorithm to my needs. I came up with the following:

if($score >= 0) {
    $sign = 1;
} elseif($score < 0) {
    $sign = -1;
}
return round( ($sign * $order) + ($seconds / 45000) , 7);

This way articles with a negative score will just lower the rank instead to invert it. (the punishment for a score of -1 for example shouldn't be: "go to nirvana!")

Upvotes: 1

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