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<?php | |
////////////////////////////////// | |
// Reddit "hot" story algorithm // | |
////////////////////////////////// | |
function hot($ups, $downs, $date) | |
{ | |
if (is_string($date)) $date = strtotime($date); | |
$s = $ups - $downs; | |
$order = log10(max(abs($s), 1)); | |
if ($s > 0) | |
$sign = 1; | |
elseif ($s < 0) | |
$sign = -1; | |
else | |
$sign = 0; | |
$seconds = $date - 1134028003; | |
return round($sign * $order + $seconds / 45000, 7); | |
} | |
///////////////////////////////////// | |
// Reddit "Best" comment algorithm // | |
///////////////////////////////////// | |
function confidence($ups, $downs) | |
{ | |
$n = $ups + $downs; | |
if ($n == 0) return 0; | |
$z = 1.281551565545; // 80% confidence | |
$phat = $ups / $n; | |
$left = $phat + 1/(2*$n)*$z*$z; | |
$right = $z*sqrt($phat*(1-$phat)/$n + $z*$z/(4*$n*$n)); | |
$under = 1+1/$n*$z*$z; | |
return ($left - $right) / $under; | |
} | |
////////////////////////////////////////////// | |
// Hacker News front page ranking algorithm // | |
////////////////////////////////////////////// | |
function calculateScore($votes, $hourAge, $gravity = 1.8) | |
{ | |
return ($votes-1) / pow(($hourAge+2), $gravity); | |
} | |
////////////////////////////////////// | |
// Zite "Popular on Zite" algorithm // | |
////////////////////////////////////// | |
function popular($ups, $downs, $hourAge, $clicks) | |
{ | |
$averageRating = confidence($ups, $downs); | |
$interest = log10((1+$clicks) / (2*$hourAge/6.0)); | |
return $averageRating * $interest; | |
} | |
// @see http://stackoverflow.com/questions/11653545/hot-content-algorithm-score-with-time-decay | |
function decay($score, $weekNo) | |
{ | |
$score = 30; | |
$baseScore = log10(max($score,1)); | |
if ($weekNo > 1) { | |
$x = $weekNo - 1; | |
$baseScore = $baseScore * exp(-8*$x*$x); | |
} | |
return $baseScore; | |
} |
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