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如何将数组中含有从属关系的元素重新排列

从数据表里取得一组二维数组，每个元素有键为 id 和 pid 的值，在不使用递归的情况下，如何按照其 pid 的值将元素移入到相应 id 元素中成为其子元素？

array(6) {
  [0] => array(3) {
    ["id"]   =>  "21"
    ["pid"]  =>  "0"
    ["name"] =>  "aaa"
  }
  [1] => array(3) {
    ["id"]   =>  "22"
    ["pid"]  =>  "0"
    ["name"] =>  "bbb"
  }
  [2] => array(3) {
    ["id"]   =>  "23"
    ["pid"]  =>  "0"
    ["name"] =>  "ccc"
  }
  [3] => array(3) {
    ["id"]   =>  "24"
    ["pid"]  =>  "23"
    ["name"] =>  "ddd"
  }
  [4] => array(3) {
    ["id"]   =>  "25"
    ["pid"]  =>  "23"
    ["name"] =>  "eee"
  }
  [5] => array(3) {
    ["id"]   =>  "26"
    ["pid"]  =>  "22"
    ["name"] =>  "fff"
  }
}

重新排列为

array(3) {
  [0] => array(3) {
    ["id"]   =>  "21"
    ["pid"]  =>  "0"
    ["name"] =>  "aaa"
  }
  [1] => array(4) {
    ["id"]   =>  "22"
    ["pid"]  =>  "0"
    ["name"] =>  "bbb"
    ["child"]=>  array(1) {
            [0] => array(3) {
                ["id"]   =>  "26"
                ["pid"]  =>  "22"
                ["name"] =>  "fff"
            }
    }
  }
  [2] => array(4) {
    ["id"]   =>  "23"
    ["pid"]  =>  "0"
    ["name"] =>  "ccc"    
    ["child"]=>  array(2) {
             [0] => array(3) {
                ["id"]   =>  "24"
                ["pid"]  =>  "23"
                ["name"] =>  "ddd"
            }
            [1] => array(3) {
                ["id"]   =>  "25"
                ["pid"]  =>  "23"
                ["name"] =>  "eee"
            }
    }
  }
}

涉及层级关系只有两层。

我想学算法的时候应该有讲过如何把递归改成循环实现。
一般递归都可以用队列+循环来实现，你先想想，空了来写程序。

你这个本来就是该循环实现的，哪里需要递归啊……

没得PHP的环境，用JS给你写个

要是看不懂 JS，C# 和 Java 看得懂不？PHP丢太久了，语法都忘了

javascriptvar data = [{
    "id": "21",
    "pid": "0",
    "name": "aaa"
}, {
    "id": "22",
    "pid": "0",
    "name": "bbb"
}, {
    "id": "23",
    "pid": "0",
    "name": "ccc"
}, {
    "id": "24",
    "pid": "23",
    "name": "ddd"
}, {
    "id": "25",
    "pid": "23",
    "name": "eee"
}, {
    "id": "26",
    "pid": "22",
    "name": "fff"
}];


var map = {}
var root = []
data.forEach(function(item) {
    map[item.id] = item;
    var parent = map[item.pid];
    if (parent) {
        parent.child = parent.child || [];
        parent.child.push(item);
    } else {
        root.push(item);
    }
});

console.log(JSON.stringify(root, null, 4));

输出

[
    {
        "id": "21",
        "pid": "0",
        "name": "aaa"
    },
    {
        "id": "22",
        "pid": "0",
        "name": "bbb",
        "child": [
            {
                "id": "26",
                "pid": "22",
                "name": "fff"
            }
        ]
    },
    {
        "id": "23",
        "pid": "0",
        "name": "ccc",
        "child": [
            {
                "id": "24",
                "pid": "23",
                "name": "ddd"
            },
            {
                "id": "25",
                "pid": "23",
                "name": "eee"
            }
        ]
    }
]

非常感谢诸位的解答。看了你们的答案还在消化。基础不扎实还要多学习。
自己参考了一下隔壁问题。实现的代码如下：

$arr = array(
    array('id'=>21, 'pid'=>0, 'name'=>'aaa'),
    array('id'=>22, 'pid'=>0, 'name'=>'bbb'),
    array('id'=>23, 'pid'=>0, 'name'=>'ccc'),
    array('id'=>24, 'pid'=>23, 'name'=>'ddd'),
    array('id'=>25, 'pid'=>23, 'name'=>'eee'),
    array('id'=>26, 'pid'=>22, 'name'=>'fff'),
    );

$temp=[];
foreach ($arr as $item)
{
    list($id,$pid,$name) = array_values($item); // 取出数组的值并分别生成变量

    if(array_key_exists($pid, $temp)) 
    // 检查临时数组$temp中是否存在键名与$pid的值相同的键
    {
        $temp[$pid]['child'][]=array('id'=>$id,'pid'=>$pid,'name'=>$name);
        // 如果存在则新增数组至临时数组中键名为 $pid 的子元素 child 内
    }else
        $temp[$id]=array('id'=>$id,'pid'=>$pid,'name'=>$name);
        // 如果不存在则新增数组至临时数组中并设定键名为 $id
}

$array = array_values($temp);
// 将临时数组中以 $id 为键名的键修改为数字索引

echo "<pre>";
print_r($array);

取值生成变量步骤有点多余，foreach 部分更新如下：

foreach ($arr as $item)
{
    if (array_key_exists($item['pid'], $temp))
    {       
        $temp[$item['pid']]['child'][]=$item;
    }else
        $temp[$item['id']]=$item;
}

先算出每个数组的顶级pid,然后再排序下。

<?php

// 原本的数组, 偷个懒用JSON还原之
$arr = json_decode('[{
    "id": "21",
    "pid": "0",
    "name": "aaa"
}, {
    "id": "22",
    "pid": "0",
    "name": "bbb"
}, {
    "id": "23",
    "pid": "0",
    "name": "ccc"
}, {
    "id": "24",
    "pid": "23",
    "name": "ddd"
}, {
    "id": "25",
    "pid": "23",
    "name": "eee"
}, {
    "id": "26",
    "pid": "22",
    "name": "fff"
}]',TRUE);

$newArr = $rtnArr = array();
$current = array_shift($arr);
while($current){
    if($current['pid']){
        if(array_key_exists($current['pid'],$newArr)){
            $newArr[$current['pid']]['child'][]= $current;
        }else{
            $newArr[$current['pid']] = array('id'=>$current['pid'],'child'=>array());
        }
    }else{
        if(array_key_exists($current['id'],$newArr)){
            array_merge($newArr[$current['id']],$current);
        }else{
            $newArr[$current['id']] = $current;
        }
    }
    $current = array_shift($arr);
}

// 更新数组和子数组的排序
ksort($newArr);
foreach($newArr as $arr){
    if(array_key_exists('child',$arr)){
        usort($arr['child'],function($a,$b){
            return $a['id'] > $b['id'] ? 1 : -1;
        });
    }
    array_push($rtnArr,$arr);
}

// 打印
print_r($rtnArr);

?>
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