php - How to get all values from one array which do not exist in another array?

Question

How to get the values from an array that are NOT in another array in PHP?

My current aproach have bad time complexity. Is there an inbuilt php function that can solve my problem?

Example:

$a1 = array(1,2,3,4);
$a2 = array(3,4,5,6,7);

Result:

[5,6,7];

Answer 1

array_diff is your friend.

Returns an array containing all the entries from array1 that are not present in any of the other arrays.

$a1 = array(1,2,3,4);
$a2 = array(3,4,5,6,7);
$result = array_diff($a2, $a1);   
print_r($result);
Array
(
    [2] => 5
    [3] => 6
    [4] => 7
)