array_diff_key

(PHP 5 >= 5.1.0, PHP 7)

Computes the difference of arrays using keys for comparison

array array_diff_key ( array $array1, array $array2 [, array $... ] )

Compares the keys from array1 against the keys from array2 and returns the difference. This function is like array_diff() except the comparison is done on the keys instead of the values.

Parameters:

array1

The array to compare from

array2

An array to compare against

...

More arrays to compare against

Returns:

Returns an array containing all the entries from array1 whose keys are not present in any of the other arrays.

Notes:

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]);.

Examples:

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, 'blue' => 6, 'yellow' => 7, 'cyan'   => 8);

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

The above example will output:

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