Difference between functions: array_diff_ukey and array_diff_uassoc - php

Question

Can someone please explain to me whats the difference between these 2 functions:
array_diff_ukey
array_diff_uassoc
They both take keys into the compare function, and based on those keys decide if the array element should be returned or not. I've checked the php manual, but to me they both seem to be doing the same thing...

Answer 1

array_diff_ukey returns those elements of the first array whose keys compare different to all keys in the second array (the semantics of the comparison being user-defined). The values associated with those keys do not play a part.
array_diff_uassoc is a "more inclusive" version of the above that also checks values: if a key in the first array compares equal to a key in the second array but the values are different, that element is also included in the result. In this case, comparison of values is not user-defined, but works as in array_diff: for two values to compare equal, their string representation must be identical.
Example, adapted from the PHP docs:
function key_compare_func($key1, $key2)
{
if ($key1 == $key2)
return 0;
else if ($key1 > $key2)
return 1;
else
return -1;
}
$array1 = array('blue' => 1, 'red' => 2, 'green' => "3", 'purple' => 4);
$array2 = array('green' => 3, 'blue' => 6, 'yellow' => 7, 'cyan' => 8);
var_dump(array_diff_ukey($array1, $array2, 'key_compare_func'));
var_dump(array_diff_uassoc($array1, $array2, 'key_compare_func'));
See it in action.
Here, array_diff_ukey will return the "red" and "purple" elements from $array1 because these keys do not compare equal to any of the keys in $array2. However array_diff_uassoc will also return the "blue" element, because even though that key exists in both arrays the associated values are different.
Note that the "green" element is not included in either result, despite the fact that the associated value is a string in $array1 and an integer in $array2.

Answer 2

From the manual:
array_diff — Computes the difference of arrays
array_diff_key — array_diff_key — Computes the difference of arrays using keys for comparison
array_diff_assoc — Computes the difference of arrays with additional index check
This additional index check means that not only the value must be the same, but also the key must be the same. So the difference between array_diff_ukey and array_diff_uassoc is that the latter checks both keys and values, while the first only checks the keys.
The addition of the u after diff_ means that you must supply a custom callback function instead of the default built-in function.
Example based on the manual (Fiddle)
<?php
header("Content-Type: text/plain");
$array1 = array('blue' => 1, 'red' => 2, 'green' => 3, 'black' => 0, 'purple' => 4);
$array2 = array('green' => 5, 'blue' => 6, 'yellow' => 7, 'cyan' => 8, 'black' => 0);
var_dump(array_diff($array1, $array2));
var_dump(array_diff_key($array1, $array2));
var_dump(array_diff_assoc($array1, $array2));
?>
Output
array(4) {
["blue"]=>
int(1)
["red"]=>
int(2)
["green"]=>
int(3)
["purple"]=>
int(4)
}
array(2) {
["red"]=>
int(2)
["purple"]=>
int(4)
}
array(4) {
["blue"]=>
int(1)
["red"]=>
int(2)
["green"]=>
int(3)
["purple"]=>
int(4)
}