How to rearrange elements with subordination in an array

Obtain a set of two-dimensional arrays from a data table. Each element has a key value of id and pid. Without recursion, how does one move an element into the corresponding id element based on its pid value to become its child element? {Code...} is rearranged to {code...}, which involves only two layers of hierarchical relationships. Obtain a set of two-dimensional arrays from a data table. Each element has a key value of id and pid. Without recursion, how does one move an element into the corresponding id element based on its pid value to become its child element?

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"  }}

Rearrange

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"            }    }  }}

There are only two layers of hierarchical relationships involved.

Reply content:

Obtain a set of two-dimensional arrays from a data table. Each element has a key value of id and pid. Without recursion, how does one move an element into the corresponding id element based on its pid value to become its child element?

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"  }}

Rearrange

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"            }    }  }}

There are only two layers of hierarchical relationships involved.

When I want to learn algorithms, I should talk about how to change recursion into loop implementation.
Generally, recursion can be implemented by queue + loop. You should first think about it and write the program with no space.

You are actually implementing this loop. Where do you need recursion ......

I don't have a PHP environment. I will write a file for you using JS.

If I don't understand JS, Do C # and Java understand it? PHP has been lost for too long, and the syntax has been forgotten.

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));

Output

[    {        "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"            }        ]    }]

Thank you for your answers. After reading your answers, you are still digesting them. If the foundation is not solid, you need to learn more.
I have referred to the next-door question. The implementation code is as follows:

$ Arr = 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); // retrieve the array value and generate the variable if (array_key_exists ($ pid, $ temp) respectively )) // check whether a key with the same key name as $ pid exists in the temporary array $ temp {$ temp [$ pid] ['child '] [] = array ('id' =>$ id, 'pid '=> $ pid, 'name' => $ name ); // If yes, add the child element named $ pid in the temporary array.} else $ temp [$ id] = array ('id' => $ id, 'pid '=> $ pid, 'name' => $ name ); // if it does not exist, add an array to the temporary array and set the key name to $ id} $ array = array_values ($ temp ); // change the key with $ id as the key name in the temporary array to a digital index echo"
";print_r($array);
The process of generating values for variables is redundant. The foreach part is updated as follows:
foreach ($arr as $item){    if (array_key_exists($item['pid'], $temp))    {               $temp[$item['pid']]['child'][]=$item;    }else        $temp[$item['id']]=$item;}
                                        
                                    
First calculate the top-level pid of each array, and then sort it.
                                        
                                    

   $ 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);} // update the sorting ksort ($ newArr) of arrays and subarrays; 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) ;}// print print_r ($ rtnArr);?>