Web traffic allocation algorithm for A/B Test

web_traffic_sampling.php

<?php
/**
 * @author Mahadir Ahmad
 * http://madet.my
 * Traffic Allocation Algorithm
 *
 */

/**
 * O(n) method of generating Binom(n,p) distributed random numbers
 * Taken from https://github.com/gburtini/Probability-Distributions-for-PHP/blob/master/src/gburtini/Distributions/Binomial.php
 *
 */
function draw($n, $p)
{
    $x = 0;

    for ($i = 0; $i < $n; $i++) {
        if ((mt_rand() / mt_getrandmax()) < $p) {
            $x = $x + 1;
        }
    }

    return $x;
}

/**
 * Use binomial random generator to draw 0 or 1
 * based on specified percentage of traffic to receive
 *
 */
function isSampleTraffic($percentage = 1)
{
    return draw(1, $percentage) == 1;
}

function simulate($hits, $percentage)
{
    $sampled_hits = [];
    foreach ($hits as $val) {
        if (isSampleTraffic($percentage)) {
            //this traffic can then be tagged with variant A/B/C/etc
            // and used to show the variant version of the test
            array_push($sampled_hits, 1);
        }
    }

    echo "End of the day result<br>";
    echo $percentage * 100 . "% Traffic<br>";
    echo "Sampled count: " . count($sampled_hits) . "<br>";
    echo "Percentage of sampled: " . count($sampled_hits) / count($hits) * 100 . "%<br><br>";
}

// Simulation

//generate 10k hits
$hits = [];
for ($i = 0; $i < 10000; $i++) {
    $hits[$i] = 1;
}


// 100% allocation 
simulate($hits, 1);
// 50% allocation 
simulate($hits, 0.5);
// 25% allocation
simulate($hits, 0.25);
// 75% allocation
simulate($hits, 0.75);
// 30% allocation
simulate($hits, 0.30);
// 15% allocation
simulate($hits, 0.15);