How to create nested array ancestors recursively in PHP

Question

I'm using PHP 7.3. I want to create a nested array that each item must contain its own ancestors.

Original Array:

[
    [
        id => 1,
        parentId => ""
    ],
    [
        id => 2,
        parentId => 1
    ],
    [
        id => 3,
        parentId => 2
    ]
]

Required Array:

[
    [
        id => 1,
        parentId => "",
        ancestors => []
    ],
    [
        id => 2,
        parentId => 1,
        ancestors => [
            [
                id => 1,
                parentId => "",
                ancestors => []
            ],
        ]
    ],
    [
        id => 3,
        parentId => 2,
        ancestors => [
                [
                    id => 1,
                    parentId => "",
                    ancestors => []
                ],
                [
                    id => 2,
                    parentId => 1,
                    ancestors => [
                        [
                            id => 1,
                            parentId => "",
                            ancestors => []
                        ],
                    ]
                ],
        ]
    ]
]

I tried to use this solution, but I think this problem is different. Any help / guidance is greatly appreciated! Thanks.

How about this https://stackoverflow.com/questions/4196157/create-array-tree-from-array-list — ArashShiri, Aug 09 '20 at 09:06
Read this post https://stackoverflow.com/questions/5157243/how-to-create-nested-php-arrays-recursively — Rahul Jha, Aug 09 '20 at 09:17
Why would you need that? You can use original ancestor by it's id (parentId of a child). — Salim Ibrohimi, Aug 09 '20 at 09:21
These are creating children, but I want to create ancestors. @ArashShiri — Amir Reza Azizi, Aug 09 '20 at 09:25
@AmirRezaAzizi Are entries always in the "ancestors first" order? i.e. Could entry 10 be an ancestor of entry 2? — Jeto, Aug 09 '20 at 09:28
Sometimes you need to change the way you want to get things done. What you're requesting is redundant and wasteful use of resources. I suggest you to reconsider what you want from your script. — Salim Ibrohimi, Aug 09 '20 at 09:31
@Jeto Yes, It will use in file manager and each item has a path. like: /var/www/html/file.php — Amir Reza Azizi, Aug 09 '20 at 09:43
@AmirRezaAzizi Not sure exactly how that answers my question though. — Jeto, Aug 09 '20 at 09:45
@SalimIbrogimov Yes, I know that it's redundant, but our team needs it for file manager and I should handle it. — Amir Reza Azizi, Aug 09 '20 at 10:01
@Jeto Yes, they are always in the "ancestors first" order and second question's answer in No. — Amir Reza Azizi, Aug 09 '20 at 10:04
Does this answer your question? [Build a tree from a flat array in PHP](https://stackoverflow.com/questions/8840319/build-a-tree-from-a-flat-array-in-php) — orustammanapov, Aug 10 '20 at 21:11
No, but the answer from Jeto is the correct way. @orustammanapov — Amir Reza Azizi, Aug 12 '20 at 08:22

Jeto · Accepted Answer · 2020-08-12T08:07:08.053

You could first make use of array_column to group your entries by ID, then array_reduce to build your new array that includes ancestors (without altering the base one):

$entriesById = array_column($array, null, 'id');
    
$entriesWithAncestors = array_reduce(
  $entriesById,

  static function (array $result, array $entry) use ($entriesById): array {
    $result[$entry['id']] = $entry + ['ancestors' => []];
    $parentId = $entry['parentId'];
    while (isset($result[$parentId])) {
      $result[$entry['id']]['ancestors'][] = $result[$parentId];
      $parentId = $entriesById[$parentId]['parentId'] ?? null;
    }
    return $result;
  }, 

  []
);

print_r($entriesWithAncestors);

Demo

Note that this assumes parent entries are always present before their children in the original array, as you mentioned in the comments.

How to create nested array ancestors recursively in PHP

1 Answers1