PHP Manual: Computes the difference of arrays

Description

array array_diff(array $array, array ...$arrays)

Compares array against one or more other arrays and returns the values in array that are not present in any of the other arrays.

Parameters

array: The array to compare from
arrays: Arrays to compare against

Return Values

Returns an array containing all the entries from array that are not present in any of the other arrays. Keys in the array array are preserved.

Changelog

Version	Description
8.0.0	This function can now be called with only one parameter. Formerly, at least two parameters have been required.

Examples

Example #1 array_diff example

<?php
$array1 = array("a" => "green", "red", "blue", "red");
$array2 = array("b" => "green", "yellow", "red");
$result = array_diff($array1, $array2);

print_r($result);
?>

Multiple occurrences in $array1 are all treated the same way. This will output :

Array
(
    [1] => blue
)

Two elements are considered equal if and only if (string) $elem1 === (string) $elem2. That is, when the string representation is the same.

Example #2 array_diff example with non-matching types

<?php
// This will generate a Notice that an array cannot be cast to a string.
$source = [1, 2, 3, 4];
$filter = [3, 4, [5], 6];
$result = array_diff($source, $filter);

// Whereas this is fine, since the objects can cast to a string.
class S {
  private $v;

  public function __construct(string $v) {
    $this->v = $v;
  }

  public function __toString() {
    return $this->v;
  }
}

$source = [new S('a'), new S('b'), new S('c')];
$filter = [new S('b'), new S('c'), new S('d')];

$result = array_diff($source, $filter);

// $result now contains one instance of S('a');
var_dump($result);
?>

To use an alternate comparison function, see array_udiff.

Notes

Note:
This function only checks one dimension of a n-dimensional array. Of course you can check deeper dimensions by using array_diff($array1[0], $array2[0]);.

array_diff