PHP array_intersect_key() function

The array_intersect_key () function in PHP is used to compute the intersection of arrays using keys for comparison. It returns an array containing all the entries from array1 which have keys that are present in all the other arrays.

Syntax

array_intersect_key (array ;$array1, array $array2 [array;$...])

Parameter

array1(required)- This parameter signifies the input array to compare from.

array2(required)- This parameter signifies the input array to compare against.

array3….(optional)- It represents more arrays to compare against

Return

This function returns an array containing all the values in array1 which have keys that are present in all the other arrays.

Example 1

"F");
echo("\nArray 2: \n");
var_export($array2);
//returning the intersection of array1 and array2 based on their keys
$result_array = array_intersect_key($array1, $array2);
echo("\nIntersection: \n");
//printing the intersection of the keys
print_r($result_array);
?> 

Output

Array 1: array (
0 => 'A',
1 => 'b',
2 => 'c',
3 => 'd',
)
Array 2: 
array (
  0 => 'A',
  1 => 'd',
  2 => 'A',
  5 => 'F',
)
 Intersection: 
 Array
 (
     [0] => A
     [1] => b
     [2] => c
 ) 

Example 2

 "Reema", 12 => "Akash", 3 => "Sukla", 4 >"Varun",5=>"Mukta",6=>"Amar");
//initializing array2
$array2 = array(1 => "Reema", 2 => "Akash", 3 => "Tisha", 4 =>"Varun");
//initializing array3
$array3 = array(11 => "Rahul", 2 => "Akash", 3 => "Tisha", 4 =>"Varun",5=>"Reema");
//computing the intersection of the keys
$intersection = array_intersect_key($array1,$array2,$array3);
//printing the intersection
print_r($intersection);
?> 

Output

Array
(
 [3] => Sukla
 [4] => Varun

) 

Example 3

1,2=>2,3=>3,4=>4,5=>5,6=>6,7=>7,8=>8,9=>9,10=>10);
//initializing array2 with odd number
$array2 = array(1=>1,3=>3,5=>5,7=>7,9=>9);
//computing the intersection of the keys
$intersection = array_intersect_key($array1,$array2);
//printing the intersection i.e., odd numbers
print_r($intersection);
?> 

Output

Array
(
[1] => 1
[3] => 3
[5] => 5
[7] => 71
[9] => 9
)