Format simple array in multidimensional

Question

I have a simple array in PHP like this :

Array
(
    [max_size_video] => 50000
    [max_size_photo] => 8000
    [token_expire] => 100
    [dns] => mydns.fr
    ...
)

I would like to convert this array to multidimensional format with underscore as a separator:

Array
(
    [max] => Array
        (
            [size] => Array
                (
                    [video] => 50000
                    [photo] => 8000
                )
        )
    [token] => Array
        (
            [expire] => 100
        )
    [dns] => mydns.fr
    ...
)

I can do this with the following ugly code :

$item = explode('_', $row);
switch (count($item)) {
  case 1:
    $array[$item[0]] = $value;
  break;
  case 2:
    $array[$item[0]][$item[1]] = $value;
  break;
  case 3:
    $array[$item[0]][$item[1]][$item[2]] = $value;
  break;
  case 3:
    $array[$item[0]][$item[1]][$item[2]][$item[3]] = $value;
  break;
  ...
}

How can I do this with a more elegant function?

Answer 1

A reference variable will save you from that wicked code bloat!

You can make iterative calls of this Stack Overflow answer from 2012.

Code: (Demo)

function assignArrayByPath(&$arr, $path, $value, $separator = '_') {
    $keys = explode($separator, $path);
    foreach ($keys as $key) {
        $arr = &$arr[$key];
    }
    $arr = $value;
}
    
foreach ($array as $key => $value) {
    unset($array[$key]);
    assignArrayByPath($array, $key, $value);
}
var_export($array);

---

Or boil it down to this: (Demo)

function assignArrayByPath(&$result, $path, $value) {
    foreach (explode('_', $path) as $key) {
        $result = &$result[$key];
    }
    $result = $value;
}

$result = [];
foreach ($array as $key => $value) {
    assignArrayByPath($result, $key, $value);
}
var_export($result);

This technique will require that you build logical (non-monkey-wrenching) paths as keys. I mean:

1. If after 'max_size_photo' => 8000, you declare 'max' => 10000, then you will get an error.
2. If after 'max_size_photo' => 8000, you declare 'max_size' => 10000, then you will erase the previously expanded (deeper) elements from the output array.

---

p.s. You can also write it without any custom functions by nesting the loops so long as you maintain the technique of using a reference variable inside of a reference variable. Trippy, right?

Code: (Demo)

$result = [];
foreach ($array as $path => $value) {
    $ref = &$result;
    foreach (explode('_', $path) as $key) {
        $ref = &$ref[$key];
    }
    $ref = $value;
}
var_export($result);

Answer 2

Mick already provided a good solution per hour question.

Bearing in mind it might have just been for illustration purposes, I noticed the switch statement has a redundant case:

 case 3:
    $array[$item[0]][$item[1]][$item[2]] = $value;
  break;
  case 3:
    $array[$item[0]][$item[1]][$item[2]][$item[3]] = $value;
  break;

Here the second case 3 is unreachable- perhaps it was a typo and should have been case 4. This won’t lead to an error but is excess lines of code that could lead to confusion for anyone reading the code- including your future self!