array_diff_key(): Difference between two arrays with respect to Keys

$new_array = array_diff_key ($array1, $array2,....);

Comparison of two or more arrays are done by using values in array_diff()

Example with two arrays

$first=array('One' =>'First','Two'=>'Second','Three'=>'Third','Four'=>'Fourth');
$second=array('One'=> 'First','Two'=>'2nd','Third'=>'3rd','Fourth'=>'Fourth');

$result1=array_diff_key($first,$second);
while (list ($key, $val) = each ($result1)) {
echo "$key -> $val <br>";
}

Three -> Third 
Four -> Fourth 

Example 1: Comparing Three Arrays

<?php
$first = array('a' => 'apple', 'b' => 'banana', 'c' => 'cherry');
$second = array('a' => 'apple', 'd' => 'date');
$third = array('b' => 'banana', 'e' => 'elderberry');
$result = array_diff_key($first, $second, $third);
print_r($result);  // Output: ['c' => 'cherry']
?>

Example 2: Using Numeric Keys

<?php
$array1 = array(1 => 'one', 2 => 'two', 3 => 'three');
$array2 = array(2 => 'two', 4 => 'four');
$result = array_diff_key($array1, $array2);
print_r($result);  // Output: [1 => 'one', 3 => 'three']
?>

Example 3: Mixed Key Types in Arrays

<?php
$array1 = array('a' => 'apple', 2 => 'banana', 'c' => 'cherry');
$array2 = array(2 => 'banana', 'b' => 'blueberry');
$result = array_diff_key($array1, $array2);
print_r($result);  // Output: ['a' => 'apple', 'c' => 'cherry']
?>

Example 4: Comparing with an Empty Array

<?php
$array1 = array('a' => 'apple', 'b' => 'banana');
$array2 = array();
$result = array_diff_key($array1, $array2);
print_r($result);  // Output: ['a' => 'apple', 'b' => 'banana']
?>