多数组求笛卡尔积

/*--------------------------------------
 *+多数组求笛卡尔积
 *--------------------------------------
 */
　　笛卡尔（Descartes）乘积又叫直积。设A、B是任意两个集合，在集合A中任意取一个元素x，在集合B中任意取一个元素y，组成一个有序对（x，y），把这样的有序对作为新的元素，他们的全体组成的集合称为集合A和集合B的直积，记为A×B，即A×B={（x，y）|x∈A且y∈B}。

function Descartes() {
    $t = func_get_args();
    if(func_num_args() == 1){
        return call_user_func_array( __FUNCTION__, $t[0] );
    }
    $a = array_shift($t);
    if(! is_array($a)){
        $a = array($a);
    }
    $a = array_chunk($a, 1);
    do {
        $r = array();
        $b = array_shift($t);
        if(! is_array($b)){
            $b = array($b);
        }
        foreach($a as $p){
            foreach(array_chunk($b, 1) as $q){
                $r[] = array_merge($p, $q);
            }
        }
        $a = $r;
    }while($t);

    return $r;
}

//示例
$arr = array(
    array(‘a1‘,‘a2‘,‘a3‘),
    ‘b‘,
    array(‘c1‘,‘c2‘),
    array(‘d1‘,‘d2‘,‘d3‘),
    //......省略其它元素（也可以是数组），
);
$r = Descartes( $arr );

var_dump($r);exit;
/*array(18) {
  [0]=>
  array(4) {
    [0]=>
    string(2) "a1"
    [1]=>
    string(1) "b"
    [2]=>
    string(2) "c1"
    [3]=>
    string(2) "d1"
  }
  [1]=>
  array(4) {
    [0]=>
    string(2) "a1"
    [1]=>
    string(1) "b"
    [2]=>
    string(2) "c1"
    [3]=>
    string(2) "d2"
  }
  [2]=>
  array(4) {
    [0]=>
    string(2) "a1"
    [1]=>
    string(1) "b"
    [2]=>
    string(2) "c1"
    [3]=>
    string(2) "d3"
  }
  [3]=>
  array(4) {
    [0]=>
    string(2) "a1"
    [1]=>
    string(1) "b"
    [2]=>
    string(2) "c2"
    [3]=>
    string(2) "d1"
  }
  [4]=>
  array(4) {
    [0]=>
    string(2) "a1"
    [1]=>
    string(1) "b"
    [2]=>
    string(2) "c2"
    [3]=>
    string(2) "d2"
  }
  [5]=>
  array(4) {
    [0]=>
    string(2) "a1"
    [1]=>
    string(1) "b"
    [2]=>
    string(2) "c2"
    [3]=>
    string(2) "d3"
  }
  [6]=>
  array(4) {
    [0]=>
    string(2) "a2"
    [1]=>
    string(1) "b"
    [2]=>
    string(2) "c1"
    [3]=>
    string(2) "d1"
  }
  [7]=>
  array(4) {
    [0]=>
    string(2) "a2"
    [1]=>
    string(1) "b"
    [2]=>
    string(2) "c1"
    [3]=>
    string(2) "d2"
  }
  [8]=>
  array(4) {
    [0]=>
    string(2) "a2"
    [1]=>
    string(1) "b"
    [2]=>
    string(2) "c1"
    [3]=>
    string(2) "d3"
  }
  [9]=>
  array(4) {
    [0]=>
    string(2) "a2"
    [1]=>
    string(1) "b"
    [2]=>
    string(2) "c2"
    [3]=>
    string(2) "d1"
  }
  [10]=>
  array(4) {
    [0]=>
    string(2) "a2"
    [1]=>
    string(1) "b"
    [2]=>
    string(2) "c2"
    [3]=>
    string(2) "d2"
  }
  [11]=>
  array(4) {
    [0]=>
    string(2) "a2"
    [1]=>
    string(1) "b"
    [2]=>
    string(2) "c2"
    [3]=>
    string(2) "d3"
  }
  [12]=>
  array(4) {
    [0]=>
    string(2) "a3"
    [1]=>
    string(1) "b"
    [2]=>
    string(2) "c1"
    [3]=>
    string(2) "d1"
  }
  [13]=>
  array(4) {
    [0]=>
    string(2) "a3"
    [1]=>
    string(1) "b"
    [2]=>
    string(2) "c1"
    [3]=>
    string(2) "d2"
  }
  [14]=>
  array(4) {
    [0]=>
    string(2) "a3"
    [1]=>
    string(1) "b"
    [2]=>
    string(2) "c1"
    [3]=>
    string(2) "d3"
  }
  [15]=>
  array(4) {
    [0]=>
    string(2) "a3"
    [1]=>
    string(1) "b"
    [2]=>
    string(2) "c2"
    [3]=>
    string(2) "d1"
  }
  [16]=>
  array(4) {
    [0]=>
    string(2) "a3"
    [1]=>
    string(1) "b"
    [2]=>
    string(2) "c2"
    [3]=>
    string(2) "d2"
  }
  [17]=>
  array(4) {
    [0]=>
    string(2) "a3"
    [1]=>
    string(1) "b"
    [2]=>
    string(2) "c2"
    [3]=>
    string(2) "d3"
  }
}
*/