Custom Implementation of array_diff_ukey Without PHP Array Functions

array_diff_ukey compares the keys of two or more arrays using a custom callback function and returns the key-value pairs from the first array whose keys are not present in the other arrays.

Here’s how to implement array_diff_ukey manually without using PHP’s built-in array functions.

Code Example:

<?php
function custom_array_diff_ukey($array1, $array2, $keyCompareCallback) {
    $result = [];

    // Loop through the first array
    foreach ($array1 as $key1 => $value1) {
        $keyExists = false;

        // Loop through the second array
        foreach ($array2 as $key2 => $value2) {
            // Use the callback to compare keys
            if (call_user_func($keyCompareCallback, $key1, $key2) === 0) {
                $keyExists = true;
                break;
            }
        }

        // If the key doesn't exist in the second array, add it to the result
        if (!$keyExists) {
            $result[$key1] = $value1;
        }
    }

    return $result;
}

// Example usage
$array1 = ['a' => 1, 'b' => 2, 'c' => 3];
$array2 = ['A' => 10, 'b' => 20, 'd' => 30];

$keyCompareCallback = function ($key1, $key2) {
    return strcasecmp($key1, $key2); // Case-insensitive comparison
};

$difference = custom_array_diff_ukey($array1, $array2, $keyCompareCallback);
print_r($difference);
?>

Array
(
    [c] => 3
)

Explanation:

1. Inputs:
   • $array1: The first array to check.
   • $array2: The array to compare keys against.
   • $keyCompareCallback: A custom callback function for key comparison.
2. Outer Loop: Iterate through $array1 to check each key.
3. Inner Loop: For each key in $array1, iterate through $array2 to find a match.
4. Key Comparison: Use call_user_func to invoke the callback function to compare keys.
5. Result Construction: If the key from $array1 is not found in $array2, add the key-value pair to $result.
6. Output: Return the $result array containing key-value pairs from $array1 that are not in $array2.

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