关于php:函数

1.分类(当分类只有2级的时候这种写好会好点)

$data = [            ["id" => 1, "name" => "shanghai", "pid" => 0],            ["id" => 2, "name" => "beijing", "pid" => 0],            ["id" => 3, "name" => "jiangsu", "pid" => 0],            ["id" => 4, "name" => "huangpu", "pid" => 1],            ["id" => 5, "name" => "dongchengqu", "pid" => 2],            ["id" => 6, "name" => "suzhou", "pid" => 3],        ];        $result = [];        foreach ($data as $value) {            $pid = $value['pid'];            if ($pid > 0) {                $result[$pid]['children'] = $value;            } else {                $value['children'] = [];                $result[$value['id']] = $value;            }        }