The array_udiff Function

The array_udiff function compares arrays and returns elements from the first array that are not present in the subsequent arrays. For element comparison, it uses a callback function that you define yourself. The first parameter is the main array for comparison, the subsequent parameters are arrays to compare against the first one.

Syntax

phparray_udiff(array1, array2, ..., callback): array;

Example

Let's compare two arrays of numbers using a callback function for comparison:

php<?php
  $arr1 = [1, 2, 3, 4, 5];
  $arr2 = [3, 4, 5, 6, 7];
  
  $res = array_udiff($arr1, $arr2, function($a, $b) {
    return $a <=> $b;
  });
  
  print_r($res);
?>

Code execution result:

php[1, 2]

Example

Let's compare arrays of strings using a custom comparison function:

php<?php
  $arr1 = ['a', 'b', 'c', 'd'];
  $arr2 = ['c', 'd', 'e', 'f'];
  
  $res = array_udiff($arr1, $arr2, function($a, $b) {
    return strcmp($a, $b);
  });
  
  print_r($res);
?>

Code execution result:

php['a', 'b']

Example

Comparison with multiple arrays:

php<?php
  $arr1 = [1, 2, 3, 4, 5];
  $arr2 = [2, 3, 4];
  $arr3 = [3, 4, 5];
  
  $res = array_udiff($arr1, $arr2, $arr3, function($a, $b) {
    return $a <=> $b;
  });
  
  print_r($res);
?>

Code execution result:

php[1]

See Also