php实现无限级分类的树形结构

数据结构和方法如下：

$items = array(1 => array('id' => 1, 'pid' => 0, 'name' => '江西省'),2 => array('id' => 2, 'pid' => 0, 'name' => '黑龙江省'),3 => array('id' => 3, 'pid' => 1, 'name' => '南昌市'),4 => array('id' => 4, 'pid' => 2, 'name' => '哈尔滨市'),5 => array('id' => 5, 'pid' => 2, 'name' => '鸡西市'),6 => array('id' => 6, 'pid' => 4, 'name' => '香坊区'),7 => array('id' => 7, 'pid' => 4, 'name' => '南岗区'),8 => array('id' => 8, 'pid' => 6, 'name' => '和兴路'),9 => array('id' => 9, 'pid' => 7, 'name' => '西大直街'),10 => array('id' => 10, 'pid' => 8, 'name' => '东北林业大学'),11 => array('id' => 11, 'pid' => 9, 'name' => '哈尔滨工业大学'),12 => array('id' => 12, 'pid' => 8, 'name' => '哈尔滨师范大学'),13 => array('id' => 13, 'pid' => 1, 'name' => '赣州市'),14 => array('id' => 14, 'pid' => 13, 'name' => '赣县'),15 => array('id' => 15, 'pid' => 13, 'name' => '于都县'),16 => array('id' => 16, 'pid' => 14, 'name' => '茅店镇'),17 => array('id' => 17, 'pid' => 14, 'name' => '大田乡'),18 => array('id' => 18, 'pid' => 16, 'name' => '义源村'),19 => array('id' => 19, 'pid' => 16, 'name' => '上坝村'),
);function tree($items){$tree = array();	//初始化树结构数据foreach($items as $value){if(isset($items[$value['pid']])){	//如果当前父级数据存在$items[$value['pid']]['son'][] = &$items[$value['id']];	//在对应父级元素添加 son 元素数据，添加的数据为当前数据}else{	//如果当前父级数据不存在$tree[] = &$items[$value['id']];	//将当前数据添加到树结构数据里}}return $tree;	
}function genTree($items) {foreach ($items as $item)$items[$item['pid']]['son'][$item['id']] = &$items[$item['id']];	//与上方法一样，只是键值不一样return isset($items[0]['son']) ? $items[0]['son'] : array();
}print_r(tree($items));
print_r(genTree($items));

返回结果如下：

Array
([0] => Array([id] => 1[pid] => 0[name] => 江西省[son] => Array([0] => Array([id] => 3[pid] => 1[name] => 南昌市)[1] => Array([id] => 13[pid] => 1[name] => 赣州市[son] => Array([0] => Array([id] => 14[pid] => 13[name] => 赣县[son] => Array([0] => Array([id] => 16[pid] => 14[name] => 茅店镇[son] => Array([0] => Array([id] => 18[pid] => 16[name] => 义源村)[1] => Array([id] => 19[pid] => 16[name] => 上坝村)))[1] => Array([id] => 17[pid] => 14[name] => 大田乡)))[1] => Array([id] => 15[pid] => 13[name] => 于都县)))))[1] => Array([id] => 2[pid] => 0[name] => 黑龙江省[son] => Array([0] => Array([id] => 4[pid] => 2[name] => 哈尔滨市[son] => Array([0] => Array([id] => 6[pid] => 4[name] => 香坊区[son] => Array([0] => Array([id] => 8[pid] => 6[name] => 和兴路[son] => Array([0] => Array([id] => 10[pid] => 8[name] => 东北林业大学)[1] => Array([id] => 12[pid] => 8[name] => 哈尔滨师范大学)))))[1] => Array([id] => 7[pid] => 4[name] => 南岗区[son] => Array([0] => Array([id] => 9[pid] => 7[name] => 西大直街[son] => Array([0] => Array([id] => 11[pid] => 9[name] => 哈尔滨工业大学)))))))[1] => Array([id] => 5[pid] => 2[name] => 鸡西市)))
)
Array
([1] => Array([id] => 1[pid] => 0[name] => 江西省[son] => Array([3] => Array([id] => 3[pid] => 1[name] => 南昌市)[13] => Array([id] => 13[pid] => 1[name] => 赣州市[son] => Array([14] => Array([id] => 14[pid] => 13[name] => 赣县[son] => Array([16] => Array([id] => 16[pid] => 14[name] => 茅店镇[son] => Array([18] => Array([id] => 18[pid] => 16[name] => 义源村)[19] => Array([id] => 19[pid] => 16[name] => 上坝村)))[17] => Array([id] => 17[pid] => 14[name] => 大田乡)))[15] => Array([id] => 15[pid] => 13[name] => 于都县)))))[2] => Array([id] => 2[pid] => 0[name] => 黑龙江省[son] => Array([4] => Array([id] => 4[pid] => 2[name] => 哈尔滨市[son] => Array([6] => Array([id] => 6[pid] => 4[name] => 香坊区[son] => Array([8] => Array([id] => 8[pid] => 6[name] => 和兴路[son] => Array([10] => Array([id] => 10[pid] => 8[name] => 东北林业大学)[12] => Array([id] => 12[pid] => 8[name] => 哈尔滨师范大学)))))[7] => Array([id] => 7[pid] => 4[name] => 南岗区[son] => Array([9] => Array([id] => 9[pid] => 7[name] => 西大直街[son] => Array([11] => Array([id] => 11[pid] => 9[name] => 哈尔滨工业大学)))))))[5] => Array([id] => 5[pid] => 2[name] => 鸡西市)))
)