PHP array_diff_key() Function

Definition and Usage

The array_diff_key() function compares the keys from array1 against the keys from array2, array3...etc and returns an array having the difference ie. the keys which are available in array1 and not available in array2, array3...etc. This function is like array_diff() function except the comparison is done based on the keys instead of the values.

Syntax

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

Parameters

Return Values

This function returns an array containing all the keys from array1 but which are not present in any of the other arrays passed to the function.

PHP Version

This function was first introduced in PHP Version 5.1.0

Example

This example returns 4 and 5 values because first three keys (0, 1 and 2) are same in both the arrays though their values are different −

<?php
   $input1 = array(1, 2, 3, 4, 5);
   $input2 = array(4, 5, 6);

   $result = array_diff_key($input1, $input2);
   print_r($result);
?>

This will produce the following result −

Array
(
    [3] => 4
    [4] => 5
)

Example

This example return empty array, because array_diff_key() compares keys and not values becuase it finds both the arrays are having same keys, though different values so it does not find any difference −

<?php
   $input4 = array(1, 2, 3);
   $input5 = array(4, 5, 6);
 
   $result = array_diff_key($input4, $input5);
   print_r($result);
?>

This will produce the following result −

Array
(
)

Example

Try out following example −

<?php
   $input1 = array("a"=>"red","b"=>"green","c"=>"blue","d"=>"yellow", "f"=>"yellow");
   $input2 = array("a"=>"red","b"=>"green","c"=>"blue");

   $result = array_diff_key($input1, $input2);
   print_r($result);
?>

This will produce the following result −

Array
(
    [d] => yellow
    [f] => yellow
)