Добавить в хелперы

[KarelWintersky]

function weightedRandom($weights, $default_key = '') 
{
        if (empty($weights)) {
            throw new \InvalidArgumentException("Incoming array is empty");
        }
        $r = mt_rand(1, array_sum($weights));
        foreach ($weights as $key => $weight) {
            $r -= $weight;
            if ($r <= 0) {
                return $key;
            }
        }

        return $default_key;
}