Sort an array with a user-defined comparison function and maintain index association

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- PHP Manual
- Array Functions
- Sort an array with a user-defined comparison function and maintain index association

# uasort

(PHP 4, PHP 5, PHP 7, PHP 8)

uasort — Sort an array with a user-defined comparison function and maintain index association

### Description

uasort(array `&$array`, callable `$callback`): true

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.

### Parameters

`array`

  The input array.

`callback`

  The 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.

  callback(mixed `$a`, mixed `$b`): int
  Caution

  Returning non-integer values from the comparison function, such as float, will result in an internal cast to int of the callback's return value. So values such as `0.99` and `0.1` will both be cast to an integer value of `0`, which will compare such values as equal.

### Return Values

Always returns `true`.

### Changelog

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`.

### Examples

Example #1 Basic uasort() example

    <?php// Comparison functionfunction 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($array);// Sort and print the resulting arrayuasort($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
    )

### See Also

- usort() - Sort an array by values using a user-defined comparison function
- uksort() - Sort an array by keys using a user-defined comparison function
- The comparison of array sorting functions