求教一维数据转多维

$s =<<< TXT
1 = 光电鼠标
2 = 机械鼠标
3 = 没有鼠标
1.1 = 黑色光电鼠标
1.2 = 红色光电鼠标
1.2.1 = 蓝牙红色光电鼠标
TXT;$res = array();
foreach(preg_split("/[\r\n]+/", $s) as $r) {
  list($k, $txt) = explode(' = ', $r);
  $p =& $res;
  foreach(explode('.', $k) as $v) {
    if(! isset($p[$v])) $p[$v] = array('txt' => $txt, 'child' => array());
    $p =& $p[$v]['child'];
  }
}print_r($res);Array
(
    [1] => Array
        (
            [txt] => 光电鼠标
            [child] => Array
                (
                    [1] => Array
                        (
                            [txt] => 黑色光电鼠标
                            [child] => Array
                                (
                                )                        )                    [2] => Array
                        (
                            [txt] => 红色光电鼠标
                            [child] => Array
                                (
                                    [1] => Array
                                        (
                                            [txt] => 蓝牙红色光电鼠标
                                            [child] => Array
                                                (
                                                )                                        )                                )                        )                )        )    [2] => Array
        (
            [txt] => 机械鼠标
            [child] => Array
                (
                )        )    [3] => Array
        (
            [txt] => 没有鼠标
            [child] => Array
                (
                )        ))