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 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
)

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    User Contributed Notes 3 notes

    up
    153
    magikMaker
    14 years ago
    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'));

    ?>
    up
    32
    yannick dot battail at gmail dot com
    14 years ago
    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
    )
    up
    2
    php at eden2 dot com
    21 years ago
    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() ;)
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