PHP 7.0.6 Released

    Sorting Arrays

    PHP has several functions that deal with sorting arrays, and this document exists to help sort it all out.

    The main differences are:

    • Some sort based on the array keys, whereas others by the values: $array['key'] = 'value';
    • Whether or not the correlation between the keys and values are maintained after the sort, which may mean the keys are reset numerically (0,1,2 ...)
    • The order of the sort: alphabetical, low to high (ascending), high to low (descending), numerical, natural, random, or user defined
    • Note: All of these sort functions act directly on the array variable itself, as opposed to returning a new sorted array
    • If any of these sort functions evaluates two members as equal then the order is undefined (the sorting is not stable).

    Sorting function attributes
    Function name Sorts by Maintains key association Order of sort Related functions
    array_multisort() value associative yes, numeric no first array or sort options array_walk()
    asort() value yes low to high arsort()
    arsort() value yes high to low asort()
    krsort() key yes high to low ksort()
    ksort() key yes low to high asort()
    natcasesort() value yes natural, case insensitive natsort()
    natsort() value yes natural natcasesort()
    rsort() value no high to low sort()
    shuffle() value no random array_rand()
    sort() value no low to high rsort()
    uasort() value yes user defined uksort()
    uksort() key yes user defined uasort()
    usort() value no user defined uasort()

    User Contributed Notes

    "Matthew Rice"
    2 years ago
    While this may seem obvious, user-defined array sorting functions ( uksort(), uasort(), usort() ) will *not* be called if the array does not have *at least two values in it*.

    The following code:                       

    <?php

    function usortTest($a, $b) {
            var_dump($a);
            var_dump($b);
        return -    1;
    }

    $test = array('val1');
    usort($test, "usortTest");

    $test2 = array('val2', 'val3');
    usort($test2, "usortTest");

    ?>

    Will output:

    string(4) "val3"
    string(4) "val2"

    The first array doesn't get sent to the function.

    Please, under no circumstance, place any logic that modifies values, or applies non-sorting business logic in these functions as they will not always be executed.
    oculiz at gmail dot com
    5 years ago
    Another way to do a case case-insensitive sort by key would simply be:

    <?php
    uksort    ($array, 'strcasecmp');
    ?>

    Since strcasecmp is already predefined in php it saves you the trouble to actually write the comparison function yourself.
    monicse09ku at yahoo dot com
    10 months ago
    // takes an array and desired key value and returns an array
    // searches through an array for a given key, if found the key that row is made the first row and the other rows are inserted accordingly.
    // the facility of this function is to get the value with a specific key of an array as the first value.

    /////////////////////////////// function starts //////////////////////////////

    function dksort($array, $case){
        if(array_key_exists($case,$array)){
            $a[$case] = $array[$case];
            foreach($array as $key=>$val){
                if($case==$key){

                }else{
                    $a[$key] = $array[$key];
                }
            }
        }

        return $a;
    }

    $d = array(
                '22'=>'jdfhgjfd',
                '33'=>'jdfhgjfd',
                '11'=>'jrtyrjfd',
                '55'=>'jrtydairjfd',
                '77'=>'jopo',
                '99'=>'jrtasajfd',
                '44'=>'jopasdwo',
                '88'=>'hdgatyuyuiuy'
                );

    $c = dksort($d, '55');
    print_r($c);

    ////////////////////////// function ends ////////////////////////////////////////
    Mssler
    10 months ago
    simple example sorting dotted version numbers

         function sortByVersionnumber($a,$b){
             $ta=explode(".",$a); $tb=explode(".",$b);
             foreach ($ta as $k => $v){
                 if (isset($tb[$k])){
                     if($ta[$k] > $tb[$k]) {
                         return 1;
                     } elseif($ta[$k] < $tb[$k]) {
                         return -1;
                     }
                 }
             }
             return 0;
         }
         function vnksort(&$array){
             uksort($array ,"sortByVersionnumber");
         }
    Dirk
    6 years ago
    If you need to perform any of these sort functions on an array containing two or more equivalent values, you can get the equivalents to fall next to each other within the overall ordering (similar to how MySQL's ORDER BY works...) instead of breaking the sort() function, by using ksort() as a second parameter to arbitrarily distinguish any equivalent values by their unique keys:

    <?php

    sort    ($array, ksort($array));

    ?>

    Seems like this effect should be built in.  At least the workaround is so short...
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