Amegatron

function popularWords($text, $amount = 5)
{
    $top = [];
    $words = preg_split('~[^[:alnum:]]+~is', strtolower($text), -1, PREG_SPLIT_NO_EMPTY);

    foreach ($words as $word) {
        if (!isset($top[$word])) {
            $top[$word] = 0;
        }
        $top[$word]++;