function getCombinAryByNum( $a, $n,$t=array()) {
if ($n == 0) {
return array($t);
}
$r = array();
for ($i=0,$l=count($a); $i <= $l-$n; $i++) {
$tmp = getCombinAryByNum( array_slice($a, $i+1, $l, false), $n-1,array_merge($t, array($a[$i])));
$r = array_merge($r, $tmp);
}
return $r;
}
$ss = getCombinAryByNum(array(1,2,3,4,5,6,7,8),2);
print_r($ss);