How to Use PHP’s array_udiff() to Find Differences Between Arrays

Function Overview

array_udiff() compares the values of two or more arrays and returns the values from the first array that are not present in any of the other arrays. It requires a user‑defined callback to determine equality of elements.

Syntax

array_udiff(array1, array2, ..., callback)

Parameters

array1

: The first array to compare. array2: The second array to compare (additional arrays may follow). callback: A callable that receives two elements and must return an integer < 0, 0, > 0 to indicate whether the first element is less than, equal to, or greater than the second.

Performance Note

The function can accept multiple arrays, but execution time grows with the number of input arrays.

Typical Use Case

In web applications, after modifying data, developers often need to know which rows have been added, changed, or removed. array_udiff() can quickly identify elements that exist in the original dataset but not in the updated one.

Example

$old_array = [1, 2, 3, 4];
$new_array = [2, 4, 6, 8];

$result = array_udiff(
    $old_array,
    $new_array,
    function ($a, $b) {
        return $a - $b;
    }
);

print_r($result);

Result Explanation

The code above outputs an array containing 1 and 3, because these values appear in $old_array but not in $new_array. This demonstrates how array_udiff() helps developers efficiently detect differences between datasets.