array_intersect_key(): Intersection of two or more arrays considering keys only

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

Example with two arrays

$first=array('One' =>1,'Two'=>2,'Three'=>3,'Four'=>'Fourth');
$second=array('One'=>1,'Two'=>2,'Third'=>3);

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

One -> 1 
Two -> 2

Example with three arrays

$first=array('One' =>1,'Two'=>2,'Three'=>3,'Four'=>'Fourth');
$second=array('One'=>1,'Two'=>2,'Third'=>3);
$third=array('One'=>1);
$result1=array_intersect_key($first,$second,$third);
while (list ($key, $val) = each ($result1)) {
echo "$key -> $val <br>";
}

One -> 1

Example: Using Associative Arrays

$array1 = ['a' => 'apple', 'b' => 'banana', 'c' => 'cherry'];
$array2 = ['a' => 'avocado', 'b' => 'blueberry'];
$result = array_intersect_key($array1, $array2);
print_r($result);
// Output: Array ( [a] => apple [b] => banana )

Example: Filtering Array by Specific Keys

$array1 = ['name' => 'John', 'age' => 25, 'gender' => 'male', 'country' => 'USA'];
$keys_to_keep = ['name' => '', 'age' => ''];
$result = array_intersect_key($array1, $keys_to_keep);
print_r($result);
// Output: Array ( [name] => John [age] => 25 )