PHP array_diff_uassoc: How to Compare Arrays with Keys

PHP array_diff_uassoc compares arrays by values and keys. You can also pass a custom function to compare keys in your own way.

Understand the array_diff_uassoc Function in PHP

The function compares one array with another array. It checks both the values and the keys.

The syntax looks like this:

array_diff_uassoc($array1, $array2, callable $key_compare_func)

• $array1: the main array.
• $array2: the array to compare against.
• $key_compare_func: a function that compares the keys.

The function returns an array. This array contains the entries from the first array that are not present in the second array.

Here is an example:

function compareKeys($a, $b) {
    if ($a === $b) return 0;
    return ($a > $b) ? 1 : -1;
}

$a1 = ["x" => 10, "y" => 20, "z" => 30];
$a2 = ["x" => 10, "y" => 25, "w" => 30];

$result = array_diff_uassoc($a1, $a2, "compareKeys");
print_r($result);

This code compares arrays by both values and keys. The result includes keys that do not match in the second array.

Here is the output:

Array
(
    [y] => 20
    [z] => 30
)

The function checks values and keys at the same time. Your custom function decides how the keys compare. The output shows the difference between arrays.

You use this function when you need a strict comparison between arrays. This includes cases where both keys and values must match exactly.

The custom function decides how the keys compare. You can define rules for equal, greater, or smaller. This gives you control over how the different result forms.

Examples of the array_diff_uassoc in PHP

Match Arrays with Same Keys:

function cmp($a, $b) {
    return strcmp($a, $b);
}

$arr1 = ["id" => 1, "age" => 20, "name" => "Sam"];
$arr2 = ["id" => 1, "age" => 22, "name" => "Sam"];

$out = array_diff_uassoc($arr1, $arr2, "cmp");
print_r($out);
/*
Array
(
    [age] => 20
)
*/

This example compares arrays with string keys. The function detects that the values under the key "age" differ. The result contains "age" => 20 because that does not match the second array.

Compare with Different Keys:

function keyCheck($a, $b) {
    return $a <=> $b;
}

$arr1 = ["a" => 100, "b" => 200, "c" => 300];
$arr2 = ["a" => 100, "b" => 200, "d" => 400];

$out = array_diff_uassoc($arr1, $arr2, "keyCheck");
print_r($out);

This example compares arrays with numeric values but different keys. The function shows "c" => 300 because the second array has no key "c":

Array
(
    [c] => 300
)

Custom Rule for Keys:

function myKeyRule($a, $b) {
    if (strtolower($a) === strtolower($b)) return 0;
    return ($a > $b) ? 1 : -1;
}

$arr1 = ["X" => 1, "Y" => 2, "Z" => 3];
$arr2 = ["x" => 1, "y" => 2, "W" => 3];

$out = array_diff_uassoc($arr1, $arr2, "myKeyRule");
print_r($out);

This example compares keys in a case-insensitive way. The function ignores case when it checks the keys. The result only includes "Z" => 3 because the second array has no "Z" or "z".

The output:

Array
(
    [Z] => 3
)

Numbers as Keys:

function compareNumKeys($a, $b) {
    return $a - $b;
}

$arr1 = [1 => "one", 2 => "two", 3 => "three"];
$arr2 = [1 => "one", 4 => "two", 5 => "three"];

$out = array_diff_uassoc($arr1, $arr2, "compareNumKeys");
print_r($out);

This example compares arrays with numbers as keys. The function detects that key 2 and 3 exist only in the first array. The result includes those unmatched pairs.

Here is the result:

Array
(
    [2] => two
    [3] => three
)

Wrapping Up

You learned what array_diff_uassoc does and how to pass a custom key comparison function. Here is a quick recap:

• The function compares arrays by values and keys.
• You pass a function to decide how keys compare.
• The result contains entries from the first array that do not exist in the second array.
• You can handle both string and numeric keys with your own rule.

FAQs

array_diff_uassoc(array $array1, array $array2, callable $key_compare_func)

function compareKeys($a, $b) {
    if ($a === $b) return 0;
    return ($a > $b) ? 1 : -1;
}
$a = ["id" => 1, "name" => "Alex"];
$b = ["id" => 1, "name" => "John"];
print_r(array_diff_uassoc($a, $b, "compareKeys"));

$a = ["x" => 10, "y" => 20];  
$b = ["x" => 10, "y" => 25];  

// Direct comparison
print_r(array_diff_assoc($a, $b));  

// Custom comparison
function cmp($a, $b){ return strcmp($a, $b); }  
print_r(array_diff_uassoc($a, $b, "cmp"));

function cmpKeys($a, $b) {
    return strcmp($a, $b);
}
$a = ["id" => 101, "flag" => true];
$b = ["id" => 101];
$c = ["flag" => true];
$result = array_diff_uassoc($a, $b, $c, "cmpKeys");
print_r($result);

Similar Reads