Basic syntax and parameter description of array_diff_key()

M66 2025-06-06

In PHP, array_diff_key() is a function used to calculate the difference set of two arrays. It returns an array containing all key-value pairs that exist in the first array but not in the second array. This function compares based on the keys of the array, not the values.

Basic syntax

 array_diff_key(array $array1, array $array2, array ...$arrays): array

Parameter description:

$array1
This is the first array to be compared.
$array2
This is the second array to be compared with $array1 . The keys in this array will be removed from $array1 .
$arrays (optional)
More arrays can be passed for comparison, array_diff_key() will remove keys from these arrays from $array1 .

Return value:

This function returns a new array containing all key-value pairs that exist in $array1 but not in $array2 or other passed arrays.

Sample code

Here is an example using the array_diff_key() function:

 <?php
$array1 = [
    "apple" => 1,
    "banana" => 2,
    "cherry" => 3
];

$array2 = [
    "banana" => 2,
    "cherry" => 3
];

$result = array_diff_key($array1, $array2);
print_r($result);
?>

Output:

 Array
(
    [apple] => 1
)

In this example, array_diff_key() compares $array1 and $array2 and returns a new array containing the key "apple" , because this key only exists in $array1 and not in $array2 .

Using multiple arrays

You can also pass multiple arrays to array_diff_key() , which compares the keys in $array1 and all other arrays, returning key-value pairs that contain key-values that exist in $array1 but are not in other arrays.

 <?php
$array1 = [
    "apple" => 1,
    "banana" => 2,
    "cherry" => 3,
    "date" => 4
];

$array2 = [
    "banana" => 2,
    "cherry" => 3
];

$array3 = [
    "apple" => 1,
    "date" => 4
];

$result = array_diff_key($array1, $array2, $array3);
print_r($result);
?>