嵌套的多维数组到单个多维数组

Question

I have found numerous examples to convert a multidimensional array to a single dimensional array. I am needing to keep the data in the arrays together, just bring them out of nesting and into the first main array.

Here is the array:

Array
(
    [0] => Array
        (
            [id] => 2
            [username] => user2
            [downline] => Array
                (
                    [0] => Array
                        (
                            [id] => 5
                            [username] => user5
                            [downline] => Array
                                (
                                    [0] => Array
                                        (
                                            [id] => 9
                                            [username] => user9
                                            [downline] => Array
                                                (
                                                    [0] => Array
                                                        (
                                                            [id] => 15
                                                            [username] => user15
                                                        )
                                                    [1] => Array
                                                        (
                                                            [id] => 16
                                                            [username] => user16
                                                        )
                                                )
                                        )
                                    [1] => Array
                                        (
                                            [id] => 10
                                            [username] => user10
                                            [downline] => Array
                                                (
                                                    [0] => Array
                                                        (
                                                            [id] => 17
                                                            [username] => user17
                                                        )
                                                )
                                        )
                                )
                        )
                )
        )
    [1] => Array
        (
            [id] => 3
            [username] => user3
            [downline] => Array
                (
                    [0] => Array
                        (
                            [id] => 6
                            [username] => user6
                            [downline] => Array
                                (
                                    [0] => Array
                                        (
                                            [id] => 11
                                            [username] => user11
                                            [downline] => Array
                                                (
                                                    [0] => Array
                                                        (
                                                            [id] => 18
                                                            [username] => user18
                                                        )
                                                )
                                        )
                                )
                        )
                )
        )
    [2] => Array
        (
            [id] => 4
            [username] => user4
            [downline] => Array
                (
                    [0] => Array
                        (
                            [id] => 7
                            [username] => user7
                            [downline] => Array
                                (
                                    [0] => Array
                                        (
                                            [id] => 12
                                            [username] => user12
                                            [downline] => Array
                                                (
                                                    [0] => Array
                                                        (
                                                            [id] => 19
                                                            [username] => user19
                                                        )
                                                )
                                        )
                                )
                        )
                    [1] => Array
                        (
                            [id] => 8
                            [username] => user8
                            [downline] => Array
                                (
                                    [0] => Array
                                        (
                                            [id] => 13
                                            [username] => user13
                                        )
                                    [1] => Array
                                        (
                                            [id] => 14
                                            [username] => user14
                                        )
                                )
                        )
                )
        )
)

This is for messaging all their team members. I don't care who they are under, I just need a full running list of all the users, so I can loop through and send them a message in the system.

So here is an example of the final array I am trying to get:

[
    [id] => 2
    [username] => user2
],
[
    [id] => 5
    [username] => user5
],
[
    [id] => 9
    [username] => user9
],
[
    [id] => 15
    [username] => user15
],
[
    [id] => 16
    [username] => user16
],
[
    [id] => 10
    [username] => user10
],
[
    [id] => 17
    [username] => user17
],
[
    [id] => 3
    [username] => user3]
],
// ... and so on

Ideally, the array keys could be their user id. This will be going in a dropdown menu where they can choose a member of their team, or they can message all of them. Something like this:

[
    1 => 'user1',
    2 => 'user2',
    9 => 'user9',
]

---

I have tried variations of array_merge, array_walk_recursive.. Everything just flattens it all into one ugly 1 dimensional array..

Something like this, which didn't work:

function flatten(array $arr) {
    return array_reduce($arr, function ($c, $a) {
        return is_array($a) ? array_merge($c, flatten($a)) : array_merge($c, [$a]);
    },
    []);
}

Answer 1

The solution using array_walk_recursive function (to gather consequtive id/username pairs):

// $arr is your initial array
$result = [];
array_walk_recursive($arr, function($v, $k) use (&$result){  
    if ($k == 'id') $result[] = ['id'=> $v];
    if ($k == 'username') {
        $result[count($result)-1]['username'] = $v;
    }
});