请教一个二维数组元素组合的算法

$arr = array(    array('a','b','c'),    array('c','f'),    array('g','z'),    array('x','y'));//$arr子集元素长度可能会多一些//将$arr的子集元素与$arr其他子集元素两两组合或者三三四四组合//子集array('a','b','c')中的元素不需要组合//两两组合$newarr = array(  array('a','c'),  array('a','f'),  array('b','c'),  array('b','f'),  array('c','c'),  array('c','f'),  ……)//三三组合$newarr = array(  array('a','c','g'),  array('a','f','g'),  array('b','c','g'),  array('b','f','g'),  array('c','c','g'),  array('c','f','g'),  ……)//四四组合$newarr = array(  array('a','c','g','x'),  array('a','f','g','x'),  array('b','c','g','x'),  array('b','f','g','x'),  array('c','c','g','x'),  array('c','f','g','x'),  ……)

//$arr：原始数组，$cNum：组合长度function getCombination($arr,$cNum){  ……}

function getCombination($arr, $cNum) {   $res = array();   foreach( Combination($arr, $cNum) as $item) {      $res = array_merge($res, Descartes($item));   }   return $res;}

function Combination( $arr, $num=0) {	$arr = array_values($arr);	$len = count($arr);	if($num <= 0 || $num > $len) $num = $len;	$res = array();	for($i=1,$n=pow(2, $len); $i<$n; ++$i) {		$tmp = str_pad(base_convert($i, 10, 2), $len, '0', STR_PAD_LEFT);		$t = array();		for($j=0; $j<$len; ++$j) {			if($tmp{$j} == '1') {				$t[] = $arr[$j];			}		}		if(count($t) == $num) $res[] = $t;	}	return $res;}function Descartes($d) {	$r = array_pop($d);	while($d) {		$t = array();		$s = array_pop($d);		if(! is_array($s)) $s = array($s);		foreach($s as $x) {			foreach($r as $y) $t[] = array_merge(array($x), is_array($y) ? $y : array($y));		}		$r = $t;	}	return $r;}