By deceze

2013-06-28 11:53:56 8 Comments

This question is intended as a reference for questions about sorting arrays in PHP. It is easy to think that your particular case is unique and worthy of a new question, but most are actually minor variations of one of the solutions on this page.

If your question is closed as a duplicate of this one, please ask for your question to be reopened only if you can explain why it differs markedly from all of the below.

How do I sort an array in PHP?
How do I sort a complex array in PHP?
How do I sort an array of objects in PHP?

  1. Basic one-dimensional arrays; Incl. Multidimensional arrays, incl. arrays of objects; Incl. Sorting one array based on another

  2. Sorting with SPL

  3. Stable sort

For the practical answer using PHP's existing functions see 1., for the academic in-detail answer on sorting algorithms (which PHP's functions implement and which you may need for really, really complex cases), see 2.


@Rizerzero 2020-03-05 19:21:44

If someone wants a simpler solution to manipulate arrays, just use Laravel Collection package which has an implemented sortBy function that lets your sort by keys simply.


i.e., in order to sort first by a, then b, then c, the correct clause would be


@mickmackusa 2019-12-04 11:48:27

This page is very comprehensive, but I want to add a bit more about the awesome utility of the spaceship operator (three way comparison operator) -- a beautiful child of PHP7+.

Using the spaceship operator to implement multiple sort conditions

This makes great strides in reducing code bloat and improving readability.

When writing your custom sort (usort()/uasort()/uksort()) function to process a multiple conditions, you only need to write balanced arrays on either side of the operator and return the outcome. No more nested condition blocks or multiple returns.

The elements from both sides of the operator will be traversed left to right, one at a time, and returning the evaluation as soon as a non-tie is encountered or when the elements have all been compared.

Sample data for my demonstrations:

$multidimArray = [
    'a' => [
        'boolean' => true,
        'natString' => 'text10',
        'object' => (object)['prop' => 2],
        'float' => -.5,
        'mixed' => []
    'b' => [
        'boolean' => true,
        'natString' => 'text12',
        'object' => (object)['prop' => 4],
        'float' => 0,
        'mixed' => null
    'c' => [
        'boolean' => false,
        'natString' => 'text100',
        'object' => (object)['prop' => 9],
        'float' => -.5,
        'mixed' => false
    'd' => [
        'boolean' => true,
        'natString' => 'text1',
        'object' => (object)['prop' => 9],
        'float' => -5,
        'mixed' => "\0"
    'e' => [
        'boolean' => false,
        'natString' => 'text2',
        'object' => (object)['prop' => 2],
        'float' => .5,
        'mixed' => ''

Demonstrations (to avoid Stackoverflow page bloat, please see the demo link for the outputs):

  • Sorting logic:

    1. boolean DESC (false = 0, true = 1, so trues before falses)
    2. float ASC

      uasort($multidimArray, function($a, $b) {
          return [$b['boolean'], $a['float']] <=> [$a['boolean'], $b['float']];
  • Sorting logic:

    1. mixed ASC
    2. object ASC
    3. boolean ASC

      uasort($multidimArray, function($a, $b) {
          return [$a['mixed'], $a['object']->prop, $a['boolean']] <=> [$b['mixed'], $b['object']->prop, $b['boolean']];
  • Sorting logic:

    1. property count of object ASC
    2. iterability of mixed DESC
    3. natString length ASC
    4. natString ASC

      uasort($multidimArray, function($a, $b) {
          return [count(get_object_vars($a['object'])), is_iterable($a['mixed']), strlen($a['natString']), $a['natString']]
                 [count(get_object_vars($b['object'])), is_iterable($b['mixed']), strlen($b['natString']), $b['natString']];

This syntax allows you to sort values, functional outcomes, deep-nested data, and sorting direction in a elegant fashion. This is definitely worth putting in your php toolbelt ...for cases when you are processing non-database data -- because of course SQL would be a much more sensible technique.

At your own discretion, from PHP7.4 you can use arrow syntax with these anonymous functions. Same script with arrow syntax.

@GAV 2019-06-14 17:27:44

If you want to order by the key value, then you can do it one line, elegant and clear. This will order by the price ascending. Uses array_multisort and array_column.

   Array([0] => Array ( [name] => eggs [price] => 1 ) [1] => Array ( [name] => coffee [price] => 9.99 ) [2] => Array ( [name] => rice [price] => 4.04 ) )

   array_multisort (array_column($array, 'price'), SORT_ASC, $array);

to produce

     Array ( [0] => Array ( [name] => eggs [price] => 1 ) [1] => Array ( [name] => rice [price] => 4.04 ) [2] => Array ( [name] => coffee [price] => 9.99 ) )

@GT_hash 2018-08-26 14:14:04

There are several ways to sort an array.I will mention some methods for doing that task.fist of all , I will give an integer array which is called as '$numbers'.

$number = array(8,9,3,4,0,1,2);

This is the normal way to creating an array. Suppose that , I want to sort that array in ascending order.For that, 'sort()' method can be used.


    $number = array(8,9,3,4,0,1,2);

   foreach ($number as $value) {
       echo $value."  ";

Now consider the output of that,

enter image description here

You can see printed number array is sorted. If you want to that number array to be sort is descending order, 'rsort()' method can be use for that task.


     $number = array(8,9,3,4,0,1,2);

     foreach ($number as $value) {
        echo $value."  ";

consider the output..

enter image description here

Now array is sorted in descending order.Ok, Let's consider an associative array.I will give an associative array(Associative array means that, An array whose each index has unique key value.) like this,

$number = array('eight'=>8,'nine'=>9,'three'=>3,'fore'=>4,'zero'=>0,'one'=>1,'two'=>2);

So ,Now I want to sort this array in ascending order according their value.'asort()' method can be used for that.


   $number = array('eight'=>8,'nine'=>9,'three'=>3,'fore'=>4,'zero'=>0,'one'=>1,'two'=>2);

   foreach ($number as $value) {
      echo $value."  ";

If sorting descending order according their value,'arsort()' method can be used. Suppose that you want to sort that array according their key value. In this , 'ksort()' method can be use.


     $number = array('eight'=>8,'nine'=>9,'three'=>3,'fore'=>4,'zero'=>0,'one'=>1,'two'=>2);

     foreach ($number as $value) {
         echo $value."  ";

Now consider the output. enter image description here

Now array is sorted according their key value.If You want to sort the array in descending order according their key value,'krsort()' method can be used.


    $number = array('eight'=>8,'nine'=>9,'three'=>3,'fore'=>4,'zero'=>0,'one'=>1,'two'=>2);

    foreach ($number as $value) {
       echo $value."  ";

Now associative array is sorted in descending order according their key value.Look at the output. enter image description here

These are the some methods for sorting an array in ascending or descending order in php.I hope to you could get an idea.Thank you!

@mickmackusa 2019-12-05 21:04:43

Doesn't Deceze already cover these insights with: "The difference between those is merely whether key-value associations are kept (the "a" functions), whether it sorts low-to-high or reverse ("r"), whether it sorts values or keys ("k") and how it compares values ("nat" vs. normal)." in the accepted answer?

@Andrew Surdu 2018-01-30 19:26:41

Multidimensional sort by key value

Natural sort of a multidimensional array by a key value and also keep the original order(do not shuffle the main keys):

function multisortByKeyValue( $k, $arr ) {
    $ids   = array();
    $index = 1;

    foreach ( $arr as $key => $row ) {
        $ids[ $key ] = intval( $row[ $k ] ) . '-' . $index . '-' . $key;
        $index ++;

    natsort( $ids );

    $arr = array_merge( $ids, $arr );

    return $arr;

Test case:

$arr = array(
    'id1' => array(
        'label'    => 'ID 1',
        'priority' => 30,
    'id2' => array(
        'label'    => 'ID 2',
        'priority' => 70,
    'id3' => array(
        'label'    => 'ID 3',
        'priority' => 20,
    'id4' => array(
        'label'    => 'ID 4',
        'priority' => 30,

$sorted = multisortByKeyValue( 'priority', $arr );

// $sorted equals to:
array (
  'id3' => array (
    'label' => 'ID 3',
    'priority' => 20,
  'id1' => array (
    'label' => 'ID 1',
    'priority' => 30,
  'id4' => array (
    'label' => 'ID 4',
    'priority' => 30,
  'id2' => array (
    'label' => 'ID 2',
    'priority' => 70,

@deceze 2013-06-28 11:53:56

Basic one dimensional arrays

$array = array(3, 5, 2, 8);

Applicable sort functions:

  • sort
  • rsort
  • asort
  • arsort
  • natsort
  • natcasesort
  • ksort
  • krsort

The difference between those is merely whether key-value associations are kept (the "a" functions), whether it sorts low-to-high or reverse ("r"), whether it sorts values or keys ("k") and how it compares values ("nat" vs. normal). See for an overview and links to further details.

Multi dimensional arrays, including arrays of objects

$array = array(
    array('foo' => 'bar', 'baz' => 42),
    array('foo' => ...,   'baz' => ...),

If you want to sort $array by the key 'foo' of each entry, you need a custom comparison function. The above sort and related functions work on simple values that they know how to compare and sort. PHP does not simply "know" what to do with a complex value like array('foo' => 'bar', 'baz' => 42) though; so you need to tell it.

To do that, you need to create a comparison function. That function takes two elements and must return 0 if these elements are considered equal, a value lower than 0 if the first value is lower and a value higher than 0 if the first value is higher. That's all that's needed:

function cmp(array $a, array $b) {
    if ($a['foo'] < $b['foo']) {
        return -1;
    } else if ($a['foo'] > $b['foo']) {
        return 1;
    } else {
        return 0;

Often, you will want to use an anonymous function as the callback. If you want to use a method or static method, see the other ways of specifying a callback in PHP.

You then use one of these functions:

Again, they only differ in whether they keep key-value associations and sort by values or keys. Read their documentation for details.

Example usage:

usort($array, 'cmp');

usort will take two items from the array and call your cmp function with them. So cmp() will be called with $a as array('foo' => 'bar', 'baz' => 42) and $b as another array('foo' => ..., 'baz' => ...). The function then returns to usort which of the values was larger or whether they were equal. usort repeats this process passing different values for $a and $b until the array is sorted. The cmp function will be called many times, at least as many times as there are values in $array, with different combinations of values for $a and $b every time.

To get used to this idea, try this:

function cmp($a, $b) {
    echo 'cmp called with $a:', PHP_EOL;
    echo 'and $b:', PHP_EOL;

All you did was define a custom way to compare two items, that's all you need. That works with all sorts of values.

By the way, this works on any value, the values don't have to be complex arrays. If you have a custom comparison you want to do, you can do it on a simple array of numbers too.

sort sorts by reference and does not return anything useful!

Note that the array sorts in place, you do not need to assign the return value to anything. $array = sort($array) will replace the array with true, not with a sorted array. Just sort($array); works.

Custom numeric comparisons

If you want to sort by the baz key, which is numeric, all you need to do is:

function cmp(array $a, array $b) {
    return $a['baz'] - $b['baz'];

Thanks to The PoWEr oF MATH this returns a value < 0, 0 or > 0 depending on whether $a is lower than, equal to or larger than $b.

Note that this won't work well for float values, since they'll be reduced to an int and lose precision. Use explicit -1, 0 and 1 return values instead.


If you have an array of objects, it works the same way:

function cmp($a, $b) {
    return $a->baz - $b->baz;


You can do anything you need inside a comparison function, including calling functions:

function cmp(array $a, array $b) {
    return someFunction($a['baz']) - someFunction($b['baz']);


A shortcut for the first string comparison version:

function cmp(array $a, array $b) {
    return strcmp($a['foo'], $b['foo']);

strcmp does exactly what's expected of cmp here, it returns -1, 0 or 1.

Spaceship operator

PHP 7 introduced the spaceship operator, which unifies and simplifies equal/smaller/larger than comparisons across types:

function cmp(array $a, array $b) {
    return $a['foo'] <=> $b['foo'];

Sorting by multiple fields

If you want to sort primarily by foo, but if foo is equal for two elements sort by baz:

function cmp(array $a, array $b) {
    if (($cmp = strcmp($a['foo'], $b['foo'])) !== 0) {
        return $cmp;
    } else {
        return $a['baz'] - $b['baz'];

For those familiar, this is equivalent to an SQL query with ORDER BY foo, baz.
Also see this very neat shorthand version and how to create such a comparison function dynamically for an arbitrary number of keys.

Sorting into a manual, static order

If you want to sort elements into a "manual order" like "foo", "bar", "baz":

function cmp(array $a, array $b) {
    static $order = array('foo', 'bar', 'baz');
    return array_search($a['foo'], $order) - array_search($b['foo'], $order);

For all the above, if you're using PHP 5.3 or higher (and you really should), use anonymous functions for shorter code and to avoid having another global function floating around:

usort($array, function (array $a, array $b) { return $a['baz'] - $b['baz']; });

That's how simple sorting a complex multi-dimensional array can be. Again, just think in terms of teaching PHP how to tell which of two items is "greater"; let PHP do the actual sorting.

Also for all of the above, to switch between ascending and descending order simply swap the $a and $b arguments around. E.g.:

return $a['baz'] - $b['baz']; // ascending
return $b['baz'] - $a['baz']; // descending

Sorting one array based on another

And then there's the peculiar array_multisort, which lets you sort one array based on another:

$array1 = array( 4,   6,   1);
$array2 = array('a', 'b', 'c');

The expected result here would be:

$array2 = array('c', 'a', 'b');  // the sorted order of $array1

Use array_multisort to get there:

array_multisort($array1, $array2);

As of PHP 5.5.0 you can use array_column to extract a column from a multi dimensional array and sort the array on that column:

array_multisort(array_column($array, 'foo'), SORT_DESC, $array);

As of PHP 7.0.0 you can also extract properties from an array of objects.

If you have more common cases, feel free to edit this answer.

@Ja͢ck 2013-06-28 12:07:02

The numeric comparison function doesn't work for float values; I'm sure you know what I mean :)

@Ja͢ck 2013-06-28 23:58:29

For the static order, I would apply array_flip() to make use of speedier position lookup, e.g. $order[$a['foo']] instead of array_search($a['foo'], $order).

@Rizier123 2016-06-02 16:30:05

Might be a bit of a big edit: but if you think it is an improvement and I included everything essential I can apply it.

@deceze 2016-06-03 01:49:12

@Rizier123 I certainly applaud the effort, it's a very good writeup; but I would prefer it if you posted it as separate answer, even if it's very similar. Your rewrite contains a lot of details (pass by reference, big table etc.), but that detail distracts from the smooth introduction to the core topic of the workings of the comparison function, IMHO. I explicitly refer to the manual several times on purpose, because that's where such detail should be looked up; no need to repeat it here and distract from the core idea I'm trying to convey.

@Rizier123 2016-06-03 15:13:02

@deceze The main challenge, since it is a reference Q&A, is to display the information as compact and readable as possible and make it easy for users to find their sorting function. I tweaked a few things: but I still have to think about it, if it is useful and valuable to post it as separate answer, since it is very similar content

@Athari 2015-06-04 00:58:03


In .NET, LINQ is frequently used for sorting, which provides a much nicer syntax over comparison functions, especially when objects need to be sorted by multiple fields. There're several ports of LINQ to PHP, including YaLinqo library*. With it, arrays can be sorted with a single line without writing complex comparison functions.

$sortedByName         = from($objects)->orderBy('$v->name');
$sortedByCount        = from($objects)->orderBy('$v->count');
$sortedByCountAndName = from($objects)->orderBy('$v->count')->thenBy('$v->name');

Comparisons can be further customized by passing a callback as a second argument, for example:

$sortedByFilenameNat  = from($objects)->orderBy('$v->filename', 'strnatcmp');

Here, '$v->count' is a shorthand for function ($v) { return $v->count; } (either can be used). These method chains return iterators, iterators can be transformed to arrays by adding ->toArray() in the end if needed.

Internally, orderBy and related methods call appropriate array sorting functions (uasort, krsort, multisort, usort etc.).

LINQ contains many more methods inspired by SQL: filtering, grouping, joining, aggregating etc. It's best suited for cases when complex transformations on arrays and objects need to be performed without relying on databases.

* developed by me, see readme for more details and comparison with other LINQ ports

@pihu 2016-05-25 07:34:51

The simplest is to use usort function to sort array without any looping : Below is an example :

   $array_compare= array("0" =>4,"1"=>2,"2"=>500,"3"=>100);

This will sort in desending order :

usort($array_compare, function($a, $b) {
        return ($b['x1'] - $a['x1']) > 0 ? 1 :-1;

This will sort in asending order :

usort($array_compare, function($a, $b) {
        return ($b['x1'] - $a['x1']) < 0 ? 1 :-1;

@deceze 2016-05-25 07:49:01

1) The example and code are inconsistent. 2) This is already explained in excruciating detail in above answers. 3) Are you possibly trying to respond to a different question?

@Ihor Burlachenko 2016-01-15 23:03:17

It is very convenient to sort arrays with sorted function from Nspl:

Basic sorting

// Sort array
$sorted = sorted([3, 1, 2]);

// Sort array in descending order
$sortedDesc = sorted([3, 1, 2], true);

Sorting by function result

// Sort array by the result of a given function (order words by length)
$sortedByLength = sorted(['bc', 'a', 'abc'], 'strlen');
$sortedByLengthDesc = sorted(['bc', 'a', 'abc'], true, 'strlen');

// Sort array by the result of user-defined function (order words by the 1st character)
$sortedByTheFirstCharacter = sorted(['bc', 'a', 'abc'], function($v) { return $v[0]; }); 

// Which is the same as
$sortedByTheFirstCharacter = sorted(['bc', 'a', 'abc'], itemGetter(0));
$sortedByTheFirstCharacterDesc = sorted(['bc', 'a', 'abc'], true, itemGetter(0));

// itemGetter(0) returns a function which takes an argument with access by index/key
// and returns the value at index 0

Sorting multidimensional array

// Sort multidimensional array (sort list of users by their names)
$users = [
    array('name' => 'Robert', 'age' => 20),
    array('name' => 'Alex', 'age' => 30),
    array('name' => 'Jack', 'age' => 25),
$sortedByName = sorted($users, itemGetter('name'));
$sortedByNameDesc = sorted($users, true, itemGetter('name'));

// itemGetter('name') returns a function which takes an argument with access by index/key
// and returns the value of the 'name' key

Sorting array of objects

// Lets assume we have class User(name, age) with properties name and age
// and public methods getName() and getAge()
$users = [
    new User('Robert', 20),
    new User('Alex', 30),
    new User('Jack', 25),

// Sort list of objects by property value (sort list of users by their name)
$sortedByName = sorted($users, propertyGetter('name'));
$sortedByNameDesc = sorted($users, true, propertyGetter('name'));

// propertyGetter('name') returns a function which takes an object
// and returns the value of its 'name' property

// Sort list of objects by method result (sort list of users by their age)
$sortedByAge = sorted($users, methodCaller('getAge'));
$sortedByAgeDesc = sorted($users, true, methodCaller('getAge'));

// methodCaller('getAge') returns a function which takes an object
// and returns the result of its getAge() method

Sorting with a comparison function

// Sort with a comparison function (order words lexicographically with strcmp)
$sortedLexicographically = sorted(['bc', 'a', 'abc'], false, null, 'strcmp');

// Sort with user-defined comparison function (order words by the 1st character)
$sortedByTheFirstCharacter = sorted(['bc', 'a', 'abc'], false, null, function($v1, $v2) {
    return chr($v1[0]) - chr($v2[0]);

You can see all these examples here.

@Baba 2013-06-28 12:11:06

Well most basic methods are already covered by deceze I would try to look at other types of sort

Sorting with SPL


class SimpleHeapSort extends SplHeap {
    public function compare($a, $b) {
        return strcmp($a, $b);

// Let's populate our heap here (data of 2009)
$heap = new SimpleHeapSort();

echo implode(PHP_EOL, iterator_to_array($heap));




The SplMaxHeap class provides the main functionalities of a heap, keeping the maximum on the top.

$heap = new SplMaxHeap();


The SplMinHeap class provides the main functionalities of a heap, keeping the minimum on the top.

$heap = new SplMinHeap ();

Other Types of Sort

Bubble Sort

From the Wikipedia article on Bubble Sort:

Bubble sort, sometimes incorrectly referred to as sinking sort, is a simple sorting algorithm that works by repeatedly stepping through the list to be sorted, comparing each pair of adjacent items and swapping them if they are in the wrong order. The pass through the list is repeated until no swaps are needed, which indicates that the list is sorted. The algorithm gets its name from the way smaller elements "bubble" to the top of the list. Because it only uses comparisons to operate on elements, it is a comparison sort. Although the algorithm is simple, most of the other sorting algorithms are more efficient for large lists.

function bubbleSort(array $array) {
    $array_size = count($array);
    for($i = 0; $i < $array_size; $i ++) {
        for($j = 0; $j < $array_size; $j ++) {
            if ($array[$i] < $array[$j]) {
                $tem = $array[$i];
                $array[$i] = $array[$j];
                $array[$j] = $tem;
    return $array;

Selection sort

From the Wikipedia article on Selection sort:

In computer science, selection sort is a sorting algorithm, specifically an in-place comparison sort. It has O(n2) time complexity, making it inefficient on large lists, and generally performs worse than the similar insertion sort. Selection sort is noted for its simplicity, and it has performance advantages over more complicated algorithms in certain situations, particularly where auxiliary memory is limited.

function selectionSort(array $array) {
    $length = count($array);
    for($i = 0; $i < $length; $i ++) {
        $min = $i;
        for($j = $i + 1; $j < $length; $j ++) {
            if ($array[$j] < $array[$min]) {
                $min = $j;
        $tmp = $array[$min];
        $array[$min] = $array[$i];
        $array[$i] = $tmp;
    return $array;

Insertion sort

From the Wikipedia article on Insertion sort:

Insertion sort is a simple sorting algorithm that builds the final sorted array (or list) one item at a time. It is much less efficient on large lists than more advanced algorithms such as quicksort, heapsort, or merge sort. However, insertion sort provides several advantages:

function insertionSort(array $array) {
    $count = count($array);
    for($i = 1; $i < $count; $i ++) {

        $j = $i - 1;
        // second element of the array
        $element = $array[$i];
        while ( $j >= 0 && $array[$j] > $element ) {
            $array[$j + 1] = $array[$j];
            $array[$j] = $element;
            $j = $j - 1;
    return $array;


From the Wikipedia article on Shellsort:

Shellsort, also known as Shell sort or Shell's method, is an in-place comparison sort. It generalizes an exchanging sort, such as insertion or bubble sort, by starting the comparison and exchange of elements with elements that are far apart before finishing with neighboring elements.

function shellSort(array $array) {
    $gaps = array(
    $gap = array_pop($gaps);
    $length = count($array);
    while ( $gap > 0 ) {
        for($i = $gap; $i < $length; $i ++) {
            $tmp = $array[$i];
            $j = $i;
            while ( $j >= $gap && $array[$j - $gap] > $tmp ) {
                $array[$j] = $array[$j - $gap];
                $j -= $gap;
            $array[$j] = $tmp;
        $gap = array_pop($gaps);
    return $array;

Comb sort

From the Wikipedia article on Comb sort:

Comb sort is a relatively simple sorting algorithm originally designed by Wlodzimierz Dobosiewicz in 1980. Later it was rediscovered by Stephen Lacey and Richard Box in 1991. Comb sort improves on bubble sort.

function combSort(array $array) {
    $gap = count($array);
    $swap = true;
    while ( $gap > 1 || $swap ) {
        if ($gap > 1)
            $gap /= 1.25;
        $swap = false;
        $i = 0;
        while ( $i + $gap < count($array) ) {
            if ($array[$i] > $array[$i + $gap]) {
                // swapping the elements.
                list($array[$i], $array[$i + $gap]) = array(
                        $array[$i + $gap],
                $swap = true;
            $i ++;
    return $array;

Merge sort

From the Wikipedia article on Merge sort:

In computer science, a merge sort (also commonly spelled mergesort) is an O(n log n) comparison-based sorting algorithm. Most implementations produce a stable sort, which means that the implementation preserves the input order of equal elements in the sorted output

function mergeSort(array $array) {
    if (count($array) <= 1)
        return $array;

    $left = mergeSort(array_splice($array, floor(count($array) / 2)));
    $right = mergeSort($array);

    $result = array();

    while ( count($left) > 0 && count($right) > 0 ) {
        if ($left[0] <= $right[0]) {
            array_push($result, array_shift($left));
        } else {
            array_push($result, array_shift($right));
    while ( count($left) > 0 )
        array_push($result, array_shift($left));

    while ( count($right) > 0 )
        array_push($result, array_shift($right));

    return $result;


From the Wikipedia article on Quicksort:

Quicksort, or partition-exchange sort, is a sorting algorithm developed by Tony Hoare that, on average, makes O(n log n) comparisons to sort n items. In the worst case, it makes O(n2) comparisons, though this behavior is rare.

function quickSort(array $array) {
    if (count($array) == 0) {
        return $array;
    $pivot = $array[0];
    $left = $right = array();
    for($i = 1; $i < count($array); $i ++) {
        if ($array[$i] < $pivot) {
            $left[] = $array[$i];
        } else {
            $right[] = $array[$i];
    return array_merge(quickSort($left), array(
    ), quickSort($right));

Permutation sort

From the Wikipedia article on Permutation sort:

Permutation sort, which proceeds by generating the possible permutations of the input array/list until discovering the sorted one.

function permutationSort($items, $perms = array()) {
    if (empty($items)) {
        if (inOrder($perms)) {
            return $perms;
    } else {
        for($i = count($items) - 1; $i >= 0; -- $i) {
            $newitems = $items;
            $newperms = $perms;
            list($foo) = array_splice($newitems, $i, 1);
            array_unshift($newperms, $foo);
            $res = permutationSort($newitems, $newperms);
            if ($res) {
                return $res;

function inOrder($array) {
    for($i = 0; $i < count($array); $i ++) {
        if (isset($array[$i + 1])) {
            if ($array[$i] > $array[$i + 1]) {
                return False;
    return True;

Radix sort

From the Wikipedia article on Radix sort:

In computer science, radix sort is a non-comparative integer sorting algorithm that sorts data with integer keys by grouping keys by the individual digits which share the same significant position and value.

// Radix Sort for 0 to 256
function radixSort($array) {
    $n = count($array);
    $partition = array();

    for($slot = 0; $slot < 256; ++ $slot) {
        $partition[] = array();

    for($i = 0; $i < $n; ++ $i) {
        $partition[$array[$i]->age & 0xFF][] = &$array[$i];

    $i = 0;

    for($slot = 0; $slot < 256; ++ $slot) {
        for($j = 0, $n = count($partition[$slot]); $j < $n; ++ $j) {
            $array[$i ++] = &$partition[$slot][$j];
    return $array;

@Baba 2013-06-28 12:18:14

@deceze you covered all the basics .. i had to look for another way to be relevant :)

@Dave 2013-06-28 12:18:45

I don't see anything wrong with the more academic sorting methods :) alot less useful for most applications but occasionally they may be asked for / required is handy to have a reference especially since I'd forgotton about most of these over time

@Alma Do 2014-05-03 21:10:13

Actually, for quick sort it is recommended to select pivot as a median of three values: first, middle and last elements. This is my example for pivot seletion. That allows to avoid worst-case reverse-sorted array (which causes O(n^2) comparisons if we'll use just first element as pivot)

@jewelhuq 2016-01-13 10:18:12

I have heard that spl work faster than normal array sorting .Is it right?

@Mike Nguyen 2016-03-10 04:03:23

I agree with Dave, nowadays, almost fw have included that why I rarely remember or use it.

@mickmackusa 2020-02-03 22:44:30

@Baba PHP now offers "array destructuring" which affords the omissions of the temporary holding variable while bubble sorting.

@Orangepill 2013-08-19 19:16:54

As of PHP 5.3 with closures it is also possible to use a closure to determine the order of your sort.

For example assuming $array is an array of objects that contain a month property.

 $orderArray = array("Jan","Feb","Mar","Apr","May","June","July","Aug","Sept","Oct","Nov","Dec");

 usort($array, function($a, $b) use ($orderArray){
       return array_search($a->month, $orderArray) - array_search($b->month, $orderArray);

@George Langley 2014-07-08 18:33:33

Just remember that this will remove any previous relative order (for instance, the first "July" object in the pre-sorted list may end up at the end of the group of July objects after sorting). See "Stable Sort" above.

@Ja͢ck 2013-06-28 13:05:42

Stable sort

Let's say you have an array like this:

['Kale', 'Kaleidoscope', 'Aardvark', 'Apple', 'Leicester', 'Lovely']

And now you want to sort on the first letter only:

usort($array, function($a, $b) {
    return strcmp($a[0], $b[0]);

The outcome is this:

['Apple', 'Aardvark', 'Kale', 'Kaleidoscope', 'Lovely', 'Leicester']

The sort wasn't stable!

The keen observer may have noticed that the array sorting algorithm (QuickSort) didn't produce a stable outcome and that the original order between words of the same first letter wasn't preserved. This case is trivial and we should have compared the whole string, but let's assume your use-case is more complicated, such as two consecutive sorts on different fields that shouldn't cancel out each other's work.

The Schwartzian transform

The Schwartzian transform, also referred to as the decorate-sort-undecorate idiom, effects a stable sort with an inherently unstable sorting algorithm.

First, you decorate each array element with another array comprising a primary key (the value) and a secondary key (its index or position):

array_walk($array, function(&$element, $index) {
    $element = array($element, $index); // decorate

This transforms the array into this:

    ['Kale', 0], ['Kaleidoscope', 1], 
    ['Aardvark', 2], ['Apple', 3], 
    ['Leicester', 4], ['Lovely', 5]

Now, we adjust the comparison step; we compare the first letter again, but if they're the same, the secondary key is used to retain the original ordering:

usort($array, function($a, $b) {
    // $a[0] and $b[0] contain the primary sort key
    // $a[1] and $b[1] contain the secondary sort key
    $tmp = strcmp($a[0][0], $b[0][0]);

    if ($tmp != 0) {
        return $tmp; // use primary key comparison results

    return $a[1] - $b[1]; // use secondary key

Afterwards, we undecorate:

array_walk($array, function(&$element) {
    $element = $element[0];

The final result:

['Aardvark', 'Apple', 'Kale', 'Kaleidoscope', 'Leicester', 'Lovely']

What about reuse?

You had to rewrite your comparison function to work with the transformed array elements; you may not want to edit your delicate comparison functions, so here's a wrapper for the comparison function:

function stablecmp($fn)
    return function($a, $b) use ($fn) {
        if (($tmp = call_user_func($fn, $a[0], $b[0])) != 0) {
            return $tmp;
        } else {
            return $a[1] - $b[1];

Let's write the sort step using this function:

usort($array, stablecmp(function($a, $b) {
    return strcmp($a[0], $b[0]);

Voila! Your pristine comparison code is back.

@Tyler Collier 2015-03-02 05:44:33

Your phrase "effects a stable sort with an inherently unstable sorting algorithm" was the ah-ha moment for me. The wikipedia page has no mention of the word stable, which seems to me to be the beauty of the transform. Shame.

@Ja͢ck 2015-03-02 05:49:07

@TylerCollier Yeah, you need to read between the lines of that Wikipedia reference ... I saved you the trouble of doing that ;-)

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