What does array_diff_uassoc() function do in php? - php

Question

I am new to php and i have read the documentation about array_diff_uassoc() function on php.net, w3schools and on other resources on the internet but failed to get what is the use of this function. According to me it is non sense function because its its documentation is so confusing.
As i know first parameter and second parameters are arrays, but what does third parameter do it takes function and it must return less than , greater than or equal to 0 and this and this. What does this nonsense documentation means ?
Following all the examples generate same result.
Example 1
function test($a,$b){
$a > $b ? 1 : -1;
}
$arrayOne = array(
"one"=>"elementOne",
"two"=>"elementTwo",
"three"=>"elementThree"
);
$arrayTwo = array(
"one"=>"elementOne",
"two"=>"elementTwo",
"three"=>"elementThree"
);
$x = array_diff_uassoc($arrayOne,$arrayTwo,'test');
Output
Array
(
[two] => elementTwo
[three] => elementThree
)
Example 2
function test($a,$b){
$a > $b ? -1 : 1;
}
$arrayOne = array(
"one"=>"elementOne",
"two"=>"elementTwo",
"three"=>"elementThree"
);
$arrayTwo = array(
"one"=>"elementOne",
"two"=>"elementTwo",
"three"=>"elementThree"
);
$x = array_diff_uassoc($arrayOne,$arrayTwo,'test');
Output
Array
(
[two] => elementTwo
[three] => elementThree
)
Example 3
function test($a,$b){
$a < $b ? 0 : 1;
}
$arrayOne = array(
"one"=>"elementOne",
"two"=>"elementTwo",
"three"=>"elementThree"
);
$arrayTwo = array(
"one"=>"elementOne",
"two"=>"elementTwo",
"three"=>"elementThree"
);
$x = array_diff_uassoc($arrayOne,$arrayTwo,'test');
Output
Array
(
[two] => elementTwo
[three] => elementThree
)
Example 4
function test($a,$b){
$a < $b ? 0 : 1;
}
$arrayOne = array(
"one"=>"elementOne",
"two"=>"elementTwo",
"three"=>"elementThree"
);
$arrayTwo = array(
"one"=>"elementOne",
"two"=>"elementTwo",
"three"=>"elementThree"
);
$x = array_diff_uassoc($arrayOne,$arrayTwo,'test');
Output
Array
(
[two] => elementTwo
[three] => elementThree
)
So what does this nonsense function means ? Can anyone tell or may be i am wrong ?

Answer 1

The comparison function allows you to create custom logic to determine whether the two entries are the same or not.
The keys in these two arrays look totally different, because they are in different languages.
$data1 = [
'red' => true,
'yellow' => true,
'green' => true,
'blue' => true,
'black' => true,
];
$data2 = [
'rouge' => true,
'jaune' => true,
'bleu' => true,
'vert' => true,
'blanc' => true,
];
But we can still do a diff against them using a custom comparison function that recognises where the two languages have equivalent values
function colourLanguageTest($a, $b) {
static $comparator = [
'red' => 'rouge',
'yellow' => 'jaune',
'green' => 'vert',
'blue' => 'bleu',
'black' => 'noir',
'white' => 'blanc',
];
if (isset($comparator[$a])) {
return $comparator[$a] != $b;
} elseif(isset($comparator[$b])) {
return $comparator[$b] != $a;
}
return true;
}
$result = array_diff_uassoc($data1, $data2, 'colourLanguageTest');
var_dump($result);
The comparison function checks for the entries in the comparator table, so it can identify that red and rouge are the same, and treat them as a match. A boolean false (0) will be returned if there is a match a boolean true (1) if there is no match.
Because this is a diff function, it filters out all entries from the first array where our custom logic returns 0 (indicating a match) and leaves only entries where our comparison logic doesn't return a 0 (ie returns 1 or -1 or 999 or -23456)
Because 'red', 'yellow', 'green' and 'blue' all have corresponding entries in the second array that match according to the language lookup, only 'black' doesn't have a corresponding entry in the second data array, so the result of our call to array_diff_uassoc() returns
array(1) {
["black"]=>
bool(true)
}

Answer 2

there must be a return value in your callback "test" function
function test($a,$b){
if ($a === $b) {
return 0;
}
return ($a > $b)? 1:-1;
}
$arrayOne = array(
"one"=>"elementOne",
"two"=>"elementTwo",
"three"=>"elementThree"
);
$arrayTwo = array(
"one"=>"elementOne",
"two"=>"elementTwo",
"three"=>"elementThree"
);