php intersection of array of slightly different objects

Question

I'm kind of new to programming and want to know if there is a short way to find the intersection of two arrays containing slightly different Objects. That's what I tried to use:

array_uintersect()

The Object are looking like this:

class object1 
{
private $_customerId;
private $_orderId;
private $_someOtherStuff;
}

and:

class object2 
{
private $_customerId;
private $_orderId;
private $_someDifferentStuff;
}

The custom function looking like this:

private function compareObjects($o1, $o2)
        {  
            return $o1->compareObjectIntersection($o2);;
        }

Using this method:

 public function compareObjectIntersection($object)
        {
            if($this->_customerId < $object->getCustomerId() || $this->_orderId < $object->getOrderId())
            {
                return -1;
            }
            elseif$this->_customerId > $object->getCustomerId() || $this->_orderId > $object->getOrderId())
            {
                return 1;
            }
            return 0;
        }

Is this possible without coding everything by myself with a lot of for-loops?

EDIT:

The idea was to get rid of all objects not containing the same pair of these two attributes:

private $_customerId; 
private $_orderId;

In the first place i get an empty array as a result

What do the objects contain as far as data and what result would you get from the objects above??? — AbraCadaver
– AbraCadaver, Commented Jun 13, 2017 at 20:45
the objects containing different stuff, mostly integer and strings. the focus is on the first two attributes. The idea was to get rid of all objects not containing the same pair of these two attributes: private $_customerId; private $_orderId; In the first place i get an empty array as a result. — Maui
– Maui, Commented Jun 13, 2017 at 20:48
Maui, instead of changing the title to "solved", on Stack Overflow you should mark the correct answer as "accepted" (the green tick mark underneath the answer's score). :) — domsson
– domsson, Commented Jun 15, 2017 at 9:26

hakre · Accepted Answer · 2017-06-13 22:25:50Z

1

You are not looking for the same objects as you have different types here, namely object1 and object2.

Instead you're looking for similiar objects in which you're looking for those which are same for customer-ID and order-ID.

This is important to note, as by only that you can say that the comparison does not belong into any of these two types, because you could place the comparison into both, object1 and object2.

In such a case where you can not clearly identify to which object type a functionality belongs to, a good rule of thumb is to place it between these objects, e.g. create a function or a new type of it's own for the operation itself.

That for a design decision.

Now about how to make such comparison of different objects easy? One way to do that is with a hash function.

Assuming that these two IDs are integers, you can create a hash for each of these different objects with a hash function:

function customer_order_hash($object) {
    return sprintf('%d/%d', $object->getCustomerId(), $object->getOrderId());
}

This hash now makes it easy to identify objects that are the same or not: The hash will be the same.

You then can make use of it, e.g. getting all objects from $array1 that have corresponding objects in $array2:

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

$result = array_uintersect($array1, $array2, 'compare_objects');

The result then contains only these objects from the first array that were found as well by such a comparison within the second array.

As you can see, there is no (written) loop at all. Just one hash function and one comparison function making use of it.

An object hash function normally works well for such comparisons (same or not). It can also work for sorting, however this example is not working for sorting.

Additional info: A built-in object hash function in PHP is spl_object_hash.

answered Jun 13, 2017 at 22:25

hakre

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8 Comments

Maui Over a year ago

Thanks alot. This looks like the best anwser. I'll try it this evening. @hakre

hakre Over a year ago

Yes please try. I dunno if this is the best suggestion for your problem as I didn't fully understand from the question what exactly is array_uintersect for in the end. However with a object hash function it is possible to index a list of objects and then compare it more easily. en.wikipedia.org/wiki/Hash_function - For the suggestion to keep objects apart another hint I can give is to Composition over Inheritance - en.wikipedia.org/wiki/Composition_over_inheritance - To support that in your own code, you can for example introduce an interface which both object1/2 implement.

Maui Over a year ago

The problem I'm using this on is slightly more complex. These objects stands for Data from databases. The intersection of these are all entrys(DB) which should happen sth with .I'm not sure if I'll have to create a new post for this, or if it is ok to post it here. The problem itselfe is, that i have 2 databases on different server and one is MySQL and one sqlite and need to keep them kind of synced. I need more space to explain it. More this evening I guess cause I'm in school till this evening.

hakre Over a year ago

You have implementation specific identity across different data-sources that have identities on their own. It's good to keep that separated from the data-objects you use to retrieve data from the database. If it's complex, consider the use of interfaces. That helps you in keeping the non-db-related code for the operations more maintainable.

Maui Over a year ago

I tried it and it is working like a charme. Thanks alot. I'll consider using more interfaces.

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