PHP array_udiff weird behavior - php

Question

I have 2 arrays, $array0 and $array1. Let's pre-fill them:
$user01 = array("no" => 1, "name" => "john");
$user02 = array("no" => 2, "name" => "lewis");
$user03 = array("no" => 3, "name" => "dan");
$array0 = array($user01, $user02, $user03, $user04);
$user11 = array("id" => 1, "name" => "john", "attr" => "foo");
$user12 = array("id" => 7, "name" => "mark", "attr" => "bar");
$array1 = array($user11, $user12);
I want to get all users from $array0 who are not in $array1, so I use array_udiff:
$diff = array_udiff($array0, $array1, function ($userA, $userB) {
return $userA['no'] == $userB['id'];
});
However, inside the anonymous compare function, if I do a var_dump of $userA and $userB, they both seem to belong to $array0, while the behavior I was expecting is for $userA to belong to $array0 and $userB to $array1.
I.e., the expected answer is [[2, "lewis"], [3, "dan"]], but I get a 'not found index': "Undefined index id" in the line of the comparison function.
Am I missing something on array_udiff behavior?

Answer 1

I'm pretty sure PHP expects the arguments to the comparison function to be interchangeable, you either need to change the array indexes to be common, or implement logic in the comparison function to deal with this.
That's not how a comparison function works.
The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.
So:
$user01 = array("id" => 1, "name" => "john"); // "no" changed to "id"
$user02 = array("id" => 2, "name" => "lewis");
$user03 = array("id" => 3, "name" => "dan");
$array0 = array($user01, $user02, $user03); // non-existant $user04 removed
$user11 = array("id" => 1, "name" => "john", "attr" => "foo");
$user12 = array("id" => 7, "name" => "mark", "attr" => "bar");
$array1 = array($user11, $user12);
$diff = array_udiff($array0, $array1, function ($userA, $userB) {
if( $userA['id'] == $userB['id'] ) { return 0; } // compare function re-jiggered
else { return $userA['id'] - $userB['id']; }
});
print_r($diff);
Yields:
Array
(
[1] => Array
(
[id] => 2
[name] => lewis
)
[2] => Array
(
[id] => 3
[name] => dan
)
)