PHP array_diff_keys() Function

Hello folks! welcome back to a new edition of our tutorial on PHP. In this tutorial guide, we are going to be studying about the PHP array_diff_key() Function.

The PHP array_diff_key() function compares the keys from array1 against the keys from array2, array3, etc. and returns an array having the difference, that is the keys that are available in array1 but unavailable in array2, array3, etc.

This function is quite similar to array_diff() function except that the comparison in this case is done based on keys instead of values

Syntax

Following below is the syntax to use this function -

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

READ: PHP array_diff_assoc() Function

Parameter Details

Sr.No	Parameter & Description
1	array1(Required) This first array will be compared with.
2	array2(Required) It is an array to be compared with the first array
3	array3(Optional) It is an array to be compared with the first array

Return Value

It returns an array containing all the keys from array1 which are not available in any other array passed to the function.

PHP Version

This function was first lunched as part of core PHP v 5.1.0.

Example1

Try the following example. This example returns 4 and 5 values because the first three keys (0, 1 and 2) are same in both 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);
?>

Output

When the above code is executed, it will produce the following result -

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

Example2

This example returns an empty array, because the array_diff_key() compares keys and not values, because it finds that both arrays are having same keys, although different values, 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);
?>

Output

When the above code is executed, it will produce the following result -

Array
(
)

Example3

Try the following example below -

<?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);
?>

Output

When the above code is executed, it will produce the following result -

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

READ: Built-in Functions in PHP

Alright guys! This is where we are going to be rounding up for this tutorial post. In our next tutorial, we are going to be discussing about the array_diff_uassoc() Function in PHP.

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