array_diff_ukey : Difference between two or more arrays by comparing keys by using callback function

array_diff_ukey(): difference using a key callback

array_diff_ukey() compares only keys and lets your callback decide whether two keys are equal. Values are ignored for deciding membership.

$first = ['A' => 10, 'b' => 20];
$second = ['a' => 99];
$result = array_diff_ukey($first, $second, 'strcasecmp');
print_r($result);

Use a comparison callback that returns an integer less than, equal to, or greater than zero.

This function takes two or more arrays as input and then returns the result array as difference.

$new_array = array_diff_ukey ($array1, $array2,....,my_function());

my_function() : is the callback function to return integer less than , equal to or greater than zero after comparing the keys.

Returns all elements of $array1 which are not present in $array2 considering keys. Keys comparison is done through call-back function my_function().

Example with two arrays

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

$first=array('One' =>'First','Two'=>'Second','Three'=>'Third','Fourth');
$second=array('One'=> 'First','Fourth','2nd');

$result=array_diff_ukey($first,$second,"my_function");
foreach ($result as $key => $val) {
echo "$key -> $val <br>";
}

Output is here.

Two -> Second 
Three -> Third

Keys of the first index are retained. ( no re-indexing done here) . The element with value Third is included in output as the index or key is not matching with $second array though the value is matching.

Example 2

function my_function($a, $b) {
    static $match = [
        'First' => 'One',
        'Second' => 'Two',
        'Third' => 'Three',
        'Fourth' => 'Four',
        'Fifth' => 'five'
    ];
    if (isset($match[$a])) {
        return $match[$a] != $b;
    } elseif(isset($match[$b])) {
        return $match[$b] != $a; 
    }
    return true; 
// 0 returned if there is a match and 1 if no match 
}

$first=array('First' =>1,'Second'=>2,'Third'=>33,'FourthH'=>4,'Fifth'=>5);
$second=array('One'=>1,'Two'=>2,'Three'=>3,'Four'=>4);
$result=array_diff_ukey($first,$second,"my_function");
foreach ($result as $key => $val) {
echo "$key -> $val <br>";
}

Output is here

FourthH -> 4 
Fifth -> 5

The function my_function() checks the entries and returns 0 if there is a match and returns 1 if no match is found.
We are comparing keys only ( not values ) so Third =>33 is matched with Three=>3 so it not appearing in output (as the difference only shown). Similarly FourthH=>4 is not matched with Four=>4 as index or key is compared ( which is not matching ) though the value 4 is matching. Hence it is included in the output.

Example 2: Case-Insensitive Key Comparison

You can use array_diff_ukey() to perform case-insensitive key comparison by defining a custom comparison function:

$arr1 = array("Key1" => 1, "Key2" => 2);
$arr2 = array("key1" => 1, "key3" => 3);

function caseInsensitiveCompare($key1, $key2) {
    return strcasecmp($key1, $key2);
}

$result = array_diff_ukey($arr1, $arr2, "caseInsensitiveCompare");
print_r($result); // Outputs: Array ( [Key2] => 2 )

Difference between arrays considering values
Array REFERENCE

Subhendu Mohapatra

Author & Instructor at plus2net

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array_diff_ukey(): Difference between two arrays comparing keys through callback function

array_diff_ukey(): difference using a key callback

Example with two arrays

Example 2

Example 2: Case-Insensitive Key Comparison

Subhendu Mohapatra