Syntax of array_diff_key in PHP
array array_diff_key(array array1, array array2[, … array arrayN])
Returns an array that contains all of the values from the first array whose keys are not present in any of the other provided arrays. The keys of the values are preserved
Example of array_diff_key
<?php
$array1 = array('blue' => 1, 'red' => 2, 'green' => 3, 'purple' => 4);
$array2 = array('green' => 5, 'yellow' => 7, 'cyan' => 8);
var_dump(array_diff_key($array1, $array2));
?>
array(3) {
["blue"]=>
int(1)
["red"]=>
int(2)
["purple"]=>
int(4)
}