Get distribution-based random element in PHP

randomWithDistribution.php

<?php

function randomWithDistribution(array $elements) {
    if(array_sum($elements) !== 100) {
        throw new \Exception('randomWithDistribution: sum of probabilities must be 100');
    }

    $random = rand(1, 100);
    $tot = 0;
	
    foreach($elements as $id => $weight) {
        $tot += $weight;
		
        if($random <= $tot) {
            return $id;
        }
    }
}


/** 
* Test
*/
//initialize the table of results
$rounds = ['a'=>0, 'b'=>0, 'c'=>0];

//populate the results by applying the function
for($i=0; $i<10000; $i++) {
    $v = randomWithDistribution(['a'=>15, 'b'=>70, 'c'=>15]);
    $rounds[$v]++;
}

//render the results
echo '<pre>';
foreach($rounds as $id => $count) {
    $percent = $count / 100 * count($rounds);
    echo str_pad($id, 2, '000', STR_PAD_LEFT), '. ', str_repeat('-', $percent), $count, ' .. ', $percent, '%<br />';
}