Map values from one flat array to another flat array by key and fallback to null where there is no corresponding value

Question

Having Two arrays need to Merge two arrays with matching their keys and rest should be empty. I have tried array_merge(), array_diff(), array_fill() but nothing helped.

Array one

Array
    (
        [5] => PHM
        [4] => ODM
        [3] => N
        [6] => M9
        [10] => RDM9
    )

array 2

Array
  (
    [0] => 01
    [1] => 02
    [2] => 03
    [3] => 04
    [4] => 05
    [5] => 06
    [6] => 07
    [7] => 08
    [8] => 09
    [9] => 10
    [10] => 11
    [11] => 12
    [12] => 13
   )

Final Output

Array
  (
    [0] => null 
    [1] => null 
    [2] => null 
    [3] => N
    [4] => ODM
    [5] => PHM
    [6] => M9
    [7] => null 
    [8] => null 
    [9] => null 
    [10] => RDM9
    [11] =>  null   
    [12] => null 
   )

Answer 1

Make array with all nulls from the 2nd array and replace by values from the 1st array

$arr2 = array_fill_keys(array_flip($arr2), null);
$new = array_replace($arr2, $arr1);
print_r($new);

Answer 2

You can pass array 2 to a foreach loop and use an if/else statment to check if the key of array 2 exists in array 1, if so set the value of element $output[$key] to NULL, else assign the value as $arr1[key]

   foreach ($arr2 as $key=> $value){
       $output[$key]=(!array_key_exists($key, $arr1)) ? NULL : $arr1[$key];
    }
    var_dump($output);

Answer 3

Here are 3 more solutions depending on developer taste. 3 Snippet Demo

Clear all of the second array values, then replace the associative elements from the first array.

var_export(
    array_replace(array_map(fn() => null, $arr2), $arr1)
);

Functionally iterate over the second array's keys and attempt to add the mapped values from the first array to the result array or fallback to null.

var_export(
    array_reduce(
        array_keys($arr2),
        fn($result, $k) => $result + [$k => $arr1[$k] ?? null],
        []
    )
);

Use a language construct to iterate over the second array's keys and attempt to add the mapped values from the first array to the result array or fallback to null.

$result = [];
foreach ($arr2 as $k => $_) {
    $result[$k] = $arr1[$k] ?? null;    
}
var_export($result);