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PHP get difference of two arrays of objects

Posted by: admin November 30, 2021 Leave a comment

Questions:

I know there is array_diff and array_udiff for comparing the difference between two arrays, but how would I do it with two arrays of objects?

array(4) {
    [0]=>
        object(stdClass)#32 (9) {
            ["id"]=>
            string(3) "205"
            ["day_id"]=>
            string(2) "12"
        }
}

My arrays are like this one, I am interested to see the difference of two arrays based on IDs.

Answers:

This is exactly what array_udiff is for. Write a function that compares two objects the way you would like, then tell array_udiff to use that function. Something like this:

function compare_objects($obj_a, $obj_b) {
  return $obj_a->id - $obj_b->id;
}

$diff = array_udiff($first_array, $second_array, 'compare_objects');

Or, if you’re using PHP >= 5.3 you can just use an anonymous function instead of declaring a function:

$diff = array_udiff($first_array, $second_array,
  function ($obj_a, $obj_b) {
    return $obj_a->id - $obj_b->id;
  }
);

###

Here’s another option, if you want to run the diff according to object instances. You would use this as your callback to array_udiff:

function compare_objects($a, $b) {
    return strcmp(spl_object_hash($a), spl_object_hash($b));
}

You’d only want to use that if you’re certain that the arrays both contain only objects – here’s my personal use case.

###

And here is another option if you wanna compare string properties (e.g. name):

$diff = array_udiff($first_array, $second_array,
  function ($obj_a, $obj_b) {
    return strcmp($obj_a->name, $obj_b->name);
  }
);

###

Here is my take on this

/**
     * Compare two objects (active record models) and return the difference. It wil skip ID from both objects as 
     * it will be obviously different
     * Note: make sure that the attributes of the first object are present in the second object, otherwise
     * this routine will give exception.
     * 
     * @param object $object1
     * @param object $object2
     * 
     * @return array difference array in key-value pair, empty array if there is no difference
     */
    public static function compareTwoObjects($object1, $object2)
    {
        $differences=[];
        foreach($object1->attributes as $key => $value) {
            if($key =='id'){
                continue;
            }
            if($object1->$key != $object2->$key){
                $differences[$key] = array(
                                            'old' => $object1->$key,
                                            'new' => $object2->$key
                                        );
            }
        }
        return $differences;
    }