<?php
$arr=
[
    ‘0‘=>[
        "id"=>2,
        "name"=>"建材",
        "pid"=>0,
        "sort"=>50
    ],
    ‘1‘=>[
        "id"=>3,
        "name"=>"餐厅",
        "pid"=>1,
        "sort"=>50
    ],
    ‘2‘=>[
        "id"=>1,
        "name"=>"家居",
        "pid"=>0,
        "sort"=>50
    ],
    ‘3‘=>[
        "id"=>4,
        "name"=>"客厅",
        "pid"=>1,
        "sort"=>50
    ],
];

function genTree($items,$pid ="pid") {
    $map  = [];
    $tree = [];
    foreach ($items as &$it){
        $map[$it[‘id‘]] = &$it;//数据的ID名生成新的引用索引树
    }
    foreach ($items as &$it){
        $parent = &$map[$it[$pid]];
        if($parent) {
            $parent[‘son‘][] = &$it;
        }else{
            $tree[] = &$it;
        }
    }
    return $tree;
}

echo ‘<pre>‘;var_export(genTree($arr));‘<pre>‘;

//array (
//    0 =>
//        array (
//            ‘id‘ => 2,
//            ‘name‘ => ‘建材‘,
//            ‘pid‘ => 0,
//            ‘sort‘ => 50,
//        ),
//    1 =>
//        array (
//            ‘id‘ => 1,
//            ‘name‘ => ‘家居‘,
//            ‘pid‘ => 0,
//            ‘sort‘ => 50,
//            ‘son‘ =>
//                array (
//                    0 =>
//                        array (
//                            ‘id‘ => 3,
//                            ‘name‘ => ‘餐厅‘,
//                            ‘pid‘ => 1,
//                            ‘sort‘ => 50,
//                        ),
//                    1 =>
//                        array (
//                            ‘id‘ => 4,
//                            ‘name‘ => ‘客厅‘,
//                            ‘pid‘ => 1,
//                            ‘sort‘ => 50,
//                        ),
//                ),
//        ),
//)