PHP Manual: Computes the difference of arrays using keys for comparison

Description

array array_diff_key(array $array, array ...$arrays)

Compares the keys from array against the keys from arrays and returns the difference. This function is like array_diff except the comparison is done on the keys instead of the values.

Parameters

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

Return Values

Returns an array containing all the entries from array whose keys are absent from all of the other arrays.

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_key example

The two keys from the key => value pairs are considered equal only if (string) $key1 === (string) $key2 . In other words a strict type check is executed so the string representation must be the same.

<?php
$array1 = array('blue' => 1, 'red' => 2, 'green' => 3, 'purple' => 4);
$array2 = array('green' => 5, 'yellow' => 7, 'cyan' => 8);

var_dump(array_diff_key($array1, $array2));
?>

The above example will output:

array(3) {
  ["blue"]=>
  int(1)
  ["red"]=>
  int(2)
  ["purple"]=>
  int(4)
}

<?php
$array1 = array('blue' => 1, 'red'  => 2, 'green' => 3, 'purple' => 4);
$array2 = array('green' => 5, 'yellow' => 7, 'cyan' => 8);
$array3 = array('blue' => 6, 'yellow' => 7, 'mauve' => 8);

var_dump(array_diff_key($array1, $array2, $array3));
?>

The above example will output:

array(2) {
  ["red"]=>
  int(2)
  ["purple"]=>
  int(4)
}

Notes

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

array_diff_key