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PHP array_udiff() function (with example)

Hey everyone,

I'm currently working on a PHP project and I came across the "array_udiff()" function. I've read the official PHP documentation, but I'm still a bit confused about how it works. Can someone please explain it to me with a simple example?

Here's what I understand so far: the "array_udiff()" function is used to compute the difference between two or more arrays by using a callback function for the comparison. However, I'm not sure how the callback function should be implemented and what exactly it does.

Any help in clarifying this would be greatly appreciated!

All Replies



I've also worked with the "array_udiff()" function in PHP and I thought I'd share my experience with it. The "array_udiff()" function is really useful when you need to find the differences between multiple arrays, using your own custom comparison logic.

Essentially, the "array_udiff()" function compares the values of the arrays by using a user-defined callback function. This callback function is responsible for implementing the comparison logic and should return a negative, positive, or zero value to determine the order of elements.

In my project, I had an array of objects, and I wanted to find the objects that were unique among multiple arrays based on a specific property. Here's a simplified example to demonstrate how it can be used:

class User {
public $id;
public $name;

public function __construct($id, $name) {
$this->id = $id;
$this->name = $name;

function compareUsers($user1, $user2) {
return $user1->id - $user2->id;

$users1 = [
new User(1, 'John'),
new User(2, 'Alice'),
new User(3, 'Bob')

$users2 = [
new User(2, 'Alice'),
new User(4, 'Jane')

$result = array_udiff($users1, $users2, 'compareUsers');

In this example, the "compareUsers()" function compares the "id" property of two objects. The resulting array, "result", would contain the User object with id 1 and name 'John', as it is present in $users1 but not in $users2.

The key thing to remember is that the callback function should take two arguments representing the values being compared and return a comparison result. You can use any comparison logic that suits your specific needs.

I hope this helps! Let me know if you have any further questions.


Hey there,

I've used the "array_udiff()" function in my PHP project before, so I can definitely help explain it to you. The "array_udiff()" function is really handy when you need to compare and find the differences between multiple arrays, using your own custom logic to determine the comparison.

The key to understanding the "array_udiff()" function lies in the callback function you provide. This callback function is responsible for comparing the values of the arrays and determining their uniqueness. It takes two arguments, let's call them "$a" and "$b", which are the values being compared.

In the callback function, you need to define your own comparison logic by implementing a comparison algorithm. The function should return a negative integer if "$a" is less than "$b", a positive integer if "$a" is greater than "$b", or zero if they are equal. This allows "array_udiff()" to correctly identify the differences between the arrays.

Let me give you a simple example to illustrate how it works. Let's say we have two arrays: $array1 and $array2. We want to find the elements present in $array1 that are not present in $array2. We can use "array_udiff()" for that:

function compareValues($a, $b) {
return $a - $b; // Custom comparison logic - subtracting values for simplicity

$array1 = [1, 2, 3, 4, 5];
$array2 = [2, 4, 6];

$result = array_udiff($array1, $array2, 'compareValues');

In this example, the callback function "compareValues()" subtracts the values of "$b" from "$a". The resulting array, "result", would contain [1, 3, 5] as these elements are present in $array1 but not in $array2.

Remember, you can use any comparison logic you need within the callback function, allowing you to perform complex comparisons based on your specific requirements.

I hope this clears things up for you! Let me know if you have any more questions.

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