<?php
/*
"recriando a roda", função explode()
By: Papadópolis (@papadopolis)
*/
function _explode($op,$str,$lim = null) {
    $output = array();
    preg_match_all("/(.*?$op|.*?$)/i",$str,$vals);
    unset($vals[0],$vals[1][count($vals[1])-1]);
    foreach($vals as $ind => $val)
        foreach($val as $exe)
            $output[] = str_replace($op,"",$exe);
    if($lim !== null) {
        if($lim>=0) {
            $alg = array();
            $tmp = $output;

            $co = 0;
            for(;;) {
                $alg[] = $output[$co];
                unset($tmp[$co]);
                if($co == $lim-1) {
                    foreach($tmp as $val)
                        $alg[$co] .= sprintf("%s%s",$op,$val);
                    break;
                }
                ++$co;
            }

            $output = $alg;
        } else {
            $f = count($output)-1;
            $l = $f-substr($lim,1);
            for(;;) {
                unset($output[$f]);
                --$f;
                if($f == $l) break;
            }
        }
    }
    return $output;
}

$str = "a,e,i,o,u,1,2,3,4,5";
$str = _explode(",",$str,3);
print_r(array_values($str));
?>