PHP - Count unique in an array of objects

Question

I have a PHP array which contains objects like this

Array
(
[0] => stdClass Object
    (
        [label] => Test 1
        [session] => 2
    )

[1] => stdClass Object
    (
        [label] => Test 2
        [session] => 2
    )

[2] => stdClass Object
    (
        [label] => Test 3
        [session] => 42
    )

[3] => stdClass Object
    (
        [label] => Test 4
        [session] => 9
    )
 )

I am trying to count the number of unique sessions within this array. I can do it when the whole thing is an array, but I am struggling to work it out when the array contains objects.

Do I need to convert the objects into arrays or is there a way of doing it with the data in its current format?

Answer 1

https://www.php.net/manual/en/function.array-column.php :

Version    Description

 7.0.0     Added the ability for the input parameter to be an array of objects.

Use array_column to generate new keys using the session column values. This effectively removes duplicate keys.

Code: (Demo)

$array = [
    (object)['label' => 'Test 1', 'session' => 2],
    (object)['label' => 'Test 2', 'session' => 2],
    (object)['label' => 'Test 3', 'session' => 42],
    (object)['label' => 'Test 4', 'session' => 9],
];
echo sizeof(array_column($array, null, 'session'));

Output:

3

Or in a loop:

foreach ($array as $obj) {
    $result[$obj->session] = null;
}
echo sizeof($result);

Both techniques avoid the extra function call of array_unique and leverage the fact that arrays cannot store duplicate keys.