PHP array_intersect_key() Function

This builtin function of PHP is used to compute the intersection of two or more arrays. The function is different from array_intersect() and array_intersect_assoc() in a way that it uses the keys for the comparison and returns the matching key elements. The function prints only those elements of the first array whose keys matches with the elements of all other arrays.
You may refer to array_intersect() and array_intersect_assoc() for better understanding.

Syntax:

array array_intersect_key($array1, $array2, $array3, $array4...)

Parameters: The array_intersect_key() function takes at least two arrays as arguments. It can take any number of arrays greater than or equal to two separated by commas (‘,’).

Return Type: The function returns another array containing the elements of the first array that are present in all other arrays passed as the parameter whose key matches with each other. If no keys matches then, a NULL array is returned.

Examples:

Input : $array1 = ("1" => "aakash", "2" => "rishav", "3" => "gaurav")
        $array2 = ("1" => "shyam", "2" => "rishi", "5" => "rishav")
        $array3 = ("1" => "aakash", "4" => "raghav", "2" => "ravi")
Output :
        Array
        (
          [1] => aakash
          [2] => rishav
        )

Below program illustrate the array_intersect_key() function. In the below program, we have used array_intersect_key() to find the intersection between arrays. Let’s look closer at the outputs of this and other functions of array_intersect() and array_intersect_assoc() to know the difference.

<?php

// PHP program to illustrate the use
// of array_intersect_key() function

$array1 = array("1" => "aakash", "2" => "rishav", "3" => "gaurav");
$array2 = array("1" => "shyam", "2" => "rishi", "5" => "rishav");
$array3 = array("1" => "aakash", "4" => "raghav", "2" => "ravi");

print_r(array_intersect_key($array1, $array2, $array3));

?>

Output:

Array
(
    [1] => aakash
    [2] => rishav
)

Reference:
http://php.net/manual/en/function.array-intersect-key.php