Simple code to implement an infinite Classification Tree

[Php] $ items = array (1 => array ('id' => 1, 'pid '=> 0, 'name' => 'jiangxi '), 2 => array ('id' => 2, 'pid '=> 0, 'name' => 'heilongjiang province '), 3 => array ('id' => 3, 'pid '=> 1, 'name' => 'nanchang City '), 4 => array ('id' => 4, 'pid '=> 2, 'name' => 'harbin '), 5 => array ('id' => 5, 'pid '=> 2, 'name' => 'jixi City '), 6 => array ('id' => 6, 'pid '=> 4, 'name' => 'xiangfang Region '), 7 => array ('id' => 7, 'pid '=> 4, 'name' => 'nangang '), 8 => array ('id' => 8, 'pid '=> 6, 'name' =>' and xinglu '), 9 => array ('id' => 9, 'pid '=> 7, 'name' => 'westbrook Street '), 10 => array ('id' => 10, 'pid '=> 8, 'name' => 'northeast forestry Emy '), 11 => array ('id' => 11, 'pid '=> 9, 'name' => 'harbin Institute of Technology '), 12 => array ('id' => 12, 'pid '=> 8, 'name' => 'harbin Normal University '), 13 => array ('id' => 13, 'pid '=> 1, 'name' => 'ganzhou City '), 14 => array ('id' => 14, 'pid '=> 13, 'name' => 'ganxian '), 15 => array ('id' => 15, 'pid '=> 13, 'name' => 'yudu County '), 16 => array ('id' => 16, 'pid '=> 14, 'name' => 'moudian Zhen '), 17 => array ('id' => 17, 'pid' => 14, 'name' => 'tagname '), 18 => array ('id' => 18, 'pid '=> 16, 'name' => 'yiyuan cune '), 19 => array ('id' => 19, 'pid '=> 16, 'name' => 'shangba cune '), 20 => array ('id' => 20, 'pid '=> 0, 'name' => 'guangdong province '), 21 => array ('id' => 21, 'pid '=> 20, 'name' => 'guangzhou'),); $ t = array (); foreach ($ items as $ id => $ item) {if ($ item ['pid ']) {$ items [$ item ['pid '] [$ item ['id'] = & $ items [$ item ['id']; $ t [] = $ id ;}} foreach ($ t as $ u) {unset ($ items [$ u]);} echo "<pre> "; print_r ($ items );