I think the example given here using classes is convoluting things too much to demonstrate what this function does.
array_udiff() will walk through array_values($a) and array_values($b) and compare each value by using the passed in callback function.
To put it another way, array_udiff() compares $a[0] to $b[0], $b[1], $b[2], and $b[3] using the provided callback function. If the callback returns zero for any of the comparisons then $a[0] will not be in the returned array from array_udiff(). It then compares $a[1] to $b[0], $b[1], $b[2], and $b[3]. Then, finally, $a[2] to $b[0], $b[1], $b[2], and $b[3].
For example, compare_ids($a[0], $b[0]) === -5 while compare_ids($a[1], $b[1]) === 0. Therefore, $a[1] is not returned from array_udiff() since it is present in $b.
<?
$a = array(
array(
'id' => 10,
'name' => 'John',
'color' => 'red',
),
array(
'id' => 20,
'name' => 'Elise',
'color' => 'blue',
),
array(
'id' => 30,
'name' => 'Mark',
'color' => 'red',
),
);
$b = array(
array(
'id' => 15,
'name' => 'Nancy',
'color' => 'black',
),
array(
'id' => 20,
'name' => 'Elise',
'color' => 'blue',
),
array(
'id' => 30,
'name' => 'Mark',
'color' => 'red',
),
array(
'id' => 40,
'name' => 'John',
'color' => 'orange',
),
);
function compare_ids($a, $b)
{
return ($a['id'] - $b['id']);
}
function compare_names($a, $b)
{
return strcmp($a['name'], $b['name']);
}
$ret = array_udiff($a, $b, 'compare_ids');
var_dump($ret);
$ret = array_udiff($b, $a, 'compare_ids');
var_dump($ret);
$ret = array_udiff($a, $b, 'compare_names');
var_dump($ret);
?>
Which returns the following.
In the first return we see that $b has no entry in it with an id of 10.
<?
array(1) {
[0]=>
array(3) {
["id"]=>
int(10)
["name"]=>
string(4) "John"
["color"]=>
string(3) "red"
}
}
?>
In the second return we see that $a has no entry in it with an id of 15 or 40.
<?
array(2) {
[0]=>
array(3) {
["id"]=>
int(15)
["name"]=>
string(5) "Nancy"
["color"]=>
string(5) "black"
}
[3]=>
array(3) {
["id"]=>
int(40)
["name"]=>
string(4) "John"
["color"]=>
string(6) "orange"
}
}
?>
In third return we see that all names in $a are in $b (even though the entry in $b whose name is 'John' is different, the anonymous function is only comparing names).
<?
array(0) {
}
?>
