Question

I am having a hard time trying recursively sort a multidimensional array on its keys. I tried with usort(), but with no success.

Sample data:

[
    'first_level' => [
        'dir_3' => [
            'subdir_1' => [
                'file_2.mp4' => (object) [
                    'name' => 'file_2.mp4',
                ],
                'file_1.mp4' => (object) [
                    'name' => 'file_1.mp4',
                ],
            ],
        ],
        'dir_1' => [
            'subdir_2' => [
                'file_6.mp4' => (object) [
                    'name' => 'file_6.mp4',
                ],
                'file_9.mp4' => (object) [
                    'name' => 'file_9.mp4',
                ],
                'file_7.mp4' => (object) [
                    'name' => 'file_7.mp4',
                ],
            ],
            'subdir_1' => [
                'file_8.mp4' => (object) [
                    'name' => 'file_8.mp4',
                ],
            ],
        ],
    ],
]

Desired result:

[
    'first_level' => [
        'dir_1' => [
            'subdir_1' => [
                'file_8.mp4' => (object) [
                    'name' => 'file_8.mp4',
                ],
            ],
            'subdir_2' => [
                'file_6.mp4' => (object) [
                    'name' => 'file_6.mp4',
                ],
                'file_7.mp4' => (object) [
                    'name' => 'file_7.mp4',
                ],
                'file_9.mp4' => (object) [
                    'name' => 'file_9.mp4',
                ],
            ],
        ],
        'dir_3' => [
            'subdir_1' => [
                'file_1.mp4' => (object) [
                    'name' => 'file_1.mp4',
                ],
                'file_2.mp4' => (object) [
                    'name' => 'file_2.mp4',
                ],
            ],
        ],
    ],
]

Answer 1

Use a recursive function to call ksort on the current level and all deeper subarrays.

function recur_ksort(&$array) {
    foreach ($array as &$value) {
        if (is_array($value))
            recur_ksort($value);
     }
     ksort($array);
}

recur_ksort($array);
var_export($array);

Demo: https://3v4l.org/Xede5