insert element to array every x position

gistfile1.php

<?php
function insertEvery($array, $element = '', $every = null){
	if ($every == null) return false;
    $index = 0;
    foreach($array as $value) {
        if (($index + 1) % $every == 0) {
            array_splice($array, $index, 0, $element);     
        }
        $index++;
    }
    return $array;
}

echo "<pre>";
$array = array("1","2","3","4","5","6","7","8","9","10","11","12","13","14","15");
var_dump(insertEvery($array));