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.

Answer 2

I have tried your code and here created sample data

$comments= array();
$comment = new stdClass;
$comment->label = 'Test 1';
$comment->session = '2';
array_push($comments, $comment);
$comment = new stdClass;
$comment->label = 'Test 2';
$comment->session = '2';
array_push($comments, $comment);
$comment = new stdClass;
$comment->label = 'Test 3';
$comment->session = '42';
array_push($comments, $comment);
$comment = new stdClass;
$comment->label = 'Test 4';
$comment->session = '9';
array_push($comments, $comment);

Here is code I tried to get the unique value. this way you can get any field unique value

$uniques = array();
foreach ($comments as $obj) {
    $uniques[$obj->session] = $obj;
}
echo "<pre>";
print_r($uniques);
echo "</pre>";

Answer 3

You could also use array_map to only keep the value of session in the array, then use array_unique to remove the duplicate entries and finally count the unique items.

If for example your array variable is called $array :

$result = array_map(function($x){
    return $x->session;
}, $array);

echo count(array_unique($result));

That will result in:

3

Demo

Answer 4

The object within an array can be accessed with $array[0] where the 0 stands for the object. To access the objects property you can do $object->session .

To go throught every objects session property you can do:

foreach ($array as $object) {
    echo $object->session . "<br/>";
}