Recursively sort keys of a multidimensional array

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

Answer 2

You need to use ksort with recursion. Demo

function recursive_ksort(&$array) {
    foreach ($array as &$v) {
        if (is_array($v)) {
            recursive_ksort($v);
        }
    }
    ksort($array);
}

recursive_ksort($array);
var_export($array);

Answer 3

function ksort_recursive(&$array)
{
    if (is_array($array)) {
        ksort($array);
        array_walk($array, 'ksort_recursive');
    }
}

It is not necessary within the recursive function to return ksort() -- this would return the unwanted success boolean value from ksort() anyhow.

Note that this function does not throw "Warning: ksort() expects parameter 1 to be array" when given a non-array - this matches my requirements but perhaps not yours. Demo: https://3v4l.org/bogAU

Answer 4

It is fair to assume that you'd like your data ti be sorted "naturally" -- meaning that the number portion of the directory and file names should be sorted numerically instead of as simple strings. Without sorting naturally, dir_10 will be moved in front of dir_2 because when comparing the 5th character of the two strings, 1 is less than 2.

Code: (Demo)

function nat_ksort_r(&$data): void
{
    if (is_array($data)) {
        ksort($data, SORT_NATURAL);
        array_walk($data, __METHOD__);
    }
}

nat_ksort_r($array);
var_export($array);

• For natural sorting, apply the SORT_NATURAL flag to the ksort() call.
• For simpler maintenance of the recursive function, recall the function using the __METHOD__ magic constant. This makes one less place to change nat_ksort_r() if you wish to call the custom function something else.
• This recursive function does not return any data; it modifies the original array by reference.
• The lowest level contains objects and this data does not get sorted by the function.

The above function can also use a classic loop instead of a functional iterator. (Demo)

function nat_ksort_r(&$data): void
{
    if (is_array($data)) {
        ksort($data, SORT_NATURAL);
        foreach ($data as &$item) {
            (__METHOD__)($item);
        }
    }
}

nat_ksort_r($array);
var_export($array);

---

You can even write the code in a completely anonymous fashion. Demo

$nat_ksort_r = function(&$data) use (&$nat_ksort_r) {
    if (is_array($data)) {
        ksort($data, SORT_NATURAL);
        foreach ($data as &$item) {
            $nat_ksort_r($item);
        }
    }
};
$nat_ksort_r($array);
var_export($array);