Convert flat PHP array to multidimensional array

Question

I have the following array structure:

[parents] => Array
    (
        [0] => Array
            (
                [id] => 1
                [user_id] => 1
                [created] => 2014-11-09 13:47:37
                [content] => This is a test discussion
                [status] => 1
                [parent] => 0
                [project_id] => 1
            )

        [1] => Array
            (
                [id] => 4
                [user_id] => 1
                [created] => 2014-11-09 13:52:02
                [content] => 456789
                [status] => 1
                [parent] => 0
                [project_id] => 1
            )

    )

[children] => Array
    (
        [0] => Array
            (
                [id] => 2
                [user_id] => 1
                [created] => 2014-11-09 13:47:53
                [content] => This is a test reply....
                [status] => 1
                [parent] => 1
                [project_id] => 1
            )

        [1] => Array
            (
                [id] => 3
                [user_id] => 1
                [created] => 2014-11-09 13:48:13
                [content] => This is a test reply....!!!
                [status] => 1
                [parent] => 1
                [project_id] => 1
            )

        [2] => Array
            (
                [id] => 5
                [user_id] => 1
                [created] => 2014-11-09 13:52:17
                [content] => 8765432
                [status] => 1
                [parent] => 4
                [project_id] => 1
            )

    )

I would like to merge them into a parent/child relationship so it looks like follows:

[parents] => Array
    (
        [0] => Array
            (
                [id] => 1
                [user_id] => 1
                [created] => 2014-11-09 13:47:37
                [content] => This is a test discussion
                [status] => 1
                [parent] => 0
                [project_id] => 1
                [children] => Array
                    (
                        [0] => Array
                            (
                                [id] => 2
                                [user_id] => 1
                                [created] => 2014-11-09 13:47:53
                                [content] => This is a test reply....
                                [status] => 1
                                [parent] => 1
                                [project_id] => 1
                            )

                        [1] => Array
                            (
                                [id] => 3
                                [user_id] => 1
                                [created] => 2014-11-09 13:48:13
                                [content] => This is a test reply....!!!
                                [status] => 1
                                [parent] => 1
                                [project_id] => 1
                            )
                        )
            )
     )

How could I go about doing that with PHP?

By iterating the children array and appending the results to the appropriate parent element - what have you tried so far? — Steve
– Steve, Commented Nov 9, 2014 at 20:56
I attempted to write something like that, but I got stuck when figuring how to add the child array to the parent array. Since I need to add it based on the parents id not the index. — Adam
– Adam, Commented Nov 9, 2014 at 21:02

damiani · Accepted Answer · 2014-11-09 22:16:13Z

1

Assuming that all ids are unique in your parents array, you can do this:

// build a new array using parent's ID values as the key, 
// to simplify searching for parent IDs. 
foreach ($parents as $key => $value){
    $merged[$value['id']] = $value;
}

foreach ($children as $child){
    $parentID = $child['parent'];
    if (array_key_exists( $parentID, $merged )) {
        // add the child array to its parent's ['children'] value
        $merged[$parentID]['children'][] = $child;
    }
}

In the resulting array $merged, the key of each parent item will be set to its id, and all children will be nested under their corresponding parents.

answered Nov 9, 2014 at 22:16

damiani

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