PHP递归（无极分类）

$items = array(
    array('id' => 1,'pid' => 0, 'name' => '一级11' ),
    array('id' => 11, 'pid' => 0, 'name' => 'www.jb51.net 一级12' ),
    array('id' => 2, 'pid' => 1, 'name' => '二级21' ),
    array('id' => 10, 'pid' => 11, 'name' => '二级22' ),
    array('id' => 3, 'pid' => 1, 'name' => '二级23' ),
    array('id' => 12, 'pid' => 11, 'name' => '二级24' ),
    array('id' => 13, 'pid' => 12, 'name' => '三级31' ),
    array('id' => 9, 'pid' => 1, 'name' => '二级25' ),
);        

function formatTree($array, $pid = 0){
    $arr = array();
    $tem = array();
    foreach ($array as $v) {
        if ($v['pid'] == $pid) {
            $tem = $this->formatTree($array, $v['id']);
            $tem && $v['son'] = $tem;
            $arr[] = $v;
        }
    }
    return $arr;
}