(PHP 4, PHP 5, PHP 7, PHP 8)
uasort — Sort an array with a user-defined comparison function and maintain index association
Sorts array in place such that its keys
maintain their correlation with the values they are associated with,
using a user-defined comparison function.
This is used mainly when sorting associative arrays where the actual element order is significant.
Note:
If two members compare as equal, they retain their original order. Prior to PHP 8.0.0, their relative order in the sorted array was undefined.
Note:
Resets array's internal pointer to the first element.
arrayThe input array.
callbackThe comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.
Always returns true.
| Version | Description |
|---|---|
| 8.2.0 |
The return type is true now; previously, it was bool.
|
| 8.0.0 |
If callback expects a parameter to be passed
by reference, this function will now emit an E_WARNING.
|
Example #1 Basic uasort() example
<?php
// Comparison function
function cmp($a, $b) {
if ($a == $b) {
return 0;
}
return ($a < $b) ? -1 : 1;
}
// Array to be sorted
$array = array('a' => 4, 'b' => 8, 'c' => -1, 'd' => -9, 'e' => 2, 'f' => 5, 'g' => 3, 'h' => -4);
print_r($array);
// Sort and print the resulting array
uasort($array, 'cmp');
print_r($array);
?>The above example will output:
Array
(
[a] => 4
[b] => 8
[c] => -1
[d] => -9
[e] => 2
[f] => 5
[g] => 3
[h] => -4
)
Array
(
[d] => -9
[h] => -4
[c] => -1
[e] => 2
[g] => 3
[a] => 4
[f] => 5
[b] => 8
)
a quick reminder on the syntax if you want to use uasort in a Class or Object:
<?php
// procedural:
uasort($collection, 'my_sort_function');
// Object Oriented
uasort($collection, array($this, 'mySortMethod'));
// Objet Oriented with static method
uasort($collection, array('self', 'myStaticSortMethod'));
?>An Example using anonymous function.
Anonymous functions make some time the code easier to understand.
<?php
$fruits = array('Orange9','Orange11','Orange10','Orange6','Orange15');
uasort ( $fruits , function ($a, $b) {
return strnatcmp($a,$b); // or other function/code
}
);
print_r($fruits);
?>
returns
Array
(
[3] => Orange6
[0] => Orange9
[2] => Orange10
[1] => Orange11
[4] => Orange15
)Is it just me, or are the examples below misleading, and actually demonstrating situations that would be more appropriate for usort()?
After trying to make sense of the uasort() description, it sounds like it's more for sorting a 1D array like this:
"john" => "$23.12"
"tim" => "$6.50"
"bob" => "$18.54"
and getting back:
"tim" => "$6.50"
"bob" => "$18.54"
"john" => $23.12"
(assuming, of course, that your sort function is lopping off the $ and evaluating as a number -- which would complicate the use of asort() ;)Since php7.0 you can replace this boilerplate
if ($a == $b) {
return 0;
}
return ($a < $b) ? -1 : 1;
with the spaceship operator:
https://www.php.net/manual/en/migration70.new-features.php#migration70.new-features.spaceship-op
return $a <=> $b;