Save difference of two arrays in another array in PHP

Question

I'm trying to save the difference of two arrays in a new one.

I've used array_diff and the code I have right now is partially working but it seems that the new array saves the elements in wrong position.

<?php 
    // Arrays to hold the numbers for this demo
    $arr1 = array(5,6,7,8);
    $arr2 = array(2,5,6);
    $arr3 = array_diff($arr1, $arr2);

    // Correct result but in wrong positions in the array
    var_dump($arr3); // array(2) { [2]=> int(7) [3]=> int(8) }
?>

How is it possible to have a value at position 2 and 3 of an array of size 2?

Any explanation on the cause of this issue is greatly appreciated, thank you.

Answer 1

Because arrays don't have to start at zero. As you can see, array_diff() will preserve keys.

If you want to reset the array keys you can use array_values():

// Arrays to hold the numbers for this demo
$arr1 = array(5,6,7,8);
$arr2 = array(2,5,6);
$arr3 = array_values(array_diff($arr1, $arr2));
var_dump($arr3);

Output:

array(2) {
  [0]=>
  int(7)
  [1]=>
  int(8)
}

Demo