The array_intersect_key function simply compares the first array with the other array or arrays based on keys. It returns an associative array that only contains the result against matching keys.

If the key in the first array is found in the rest of the arrays, it is included in the resultant array.

What is the syntax of array_interse functionct_key in PHP?

array_intersect_key(array1, array2, array3, ...)

Parameters	Details
array1	Array to make comparison from – Required
array2	Array to compare with – Required
array3,…	Further arrays to compare with – Required

Examples of array_intersect_key function

<?php
$a1=array("a"=>"red","b"=>"green","c"=>"blue");
$a2=array("a"=>"red","c"=>"blue","d"=>"pink");

$result=array_intersect_key($a1,$a2);
print_r($result);
?>

In the above example, the array_intersect function compares only the keys of two arrays and returns the matches.

<?php
$a1=array("red","green","blue","yellow");
$a2=array("red","green","blue");

$result=array_intersect_key($a1,$a2);
print_r($result);
?>

In the above example, we use the array_intersect_key function with an indexed array. The elements of each indexed array are now treated as the keys. Therefore, the function compares them with the second array and returns the matches.

<?php
$a1=array("a"=>"red","b"=>"green","c"=>"blue");
$a2=array("c"=>"yellow","d"=>"black","e"=>"brown");
$a3=array("f"=>"green","c"=>"purple","g"=>"red");

$result=array_intersect_key($a1,$a2,$a3);
print_r($result);
?>

In the above example, the array_intersect function compares only the keys of three arrays and returns the matches.