Last updated: Fri, 05 Sep 2008

natsort

(PHP 4, PHP 5)

natsort — Sort an array using a "natural order" algorithm

Description

bool natsort ( array &$array )

This function implements a sort algorithm that orders alphanumeric strings in the way a human being would while maintaining key/value associations. This is described as a "natural ordering". An example of the difference between this algorithm and the regular computer string sorting algorithms (used in sort()) can be seen in the example below.

Parameters

array: The input array.

Return Values

Returns TRUE on success or FALSE on failure.

Examples

Example #1 natsort() example


<?php
$array1 = $array2 = array("img12.png", "img10.png", "img2.png", "img1.png");

sort($array1);
echo "Standard sorting\n";
print_r($array1);

natsort($array2);
echo "\nNatural order sorting\n";
print_r($array2);
?>

The above example will output:

Standard sorting
Array
(
    [0] => img1.png
    [1] => img10.png
    [2] => img12.png
    [3] => img2.png
)

Natural order sorting
Array
(
    [3] => img1.png
    [2] => img2.png
    [1] => img10.png
    [0] => img12.png
)

For more information see: Martin Pool's » Natural Order String Comparison page.


Here is a natsort that will sort the array based on keys (it is similar to the function posted earlier on 04-May-2006).



<?php



function knatsort(&$karr){

    $kkeyarr = array_keys($karr);

    natsort($kkeyarr);

    $ksortedarr = array();

    foreach($kkeyarr as $kcurrkey){

        $ksortedarr[$kcurrkey] = $karr[$kcurrkey];

    }

    $karr = $ksortedarr;

    return true;

}



?>

awizemann at gmail dot com
30-Aug-2007 04:34


natsort() will not work correctly if you use underscores in file names (if your array is for sorting files).



Example:



$images = array('image_1.jpg','image_12.jpg');



Will not produce the same as:



$images = array('image1.jpg','image12.jpg');

lacent at gmail dot com
16-Jan-2007 02:42


there is another rnatsort function lower on the page, but it didn't work in the context i needed it in. 



reasoning for this:

sorting naturally via the keys of an array, but needing to reverse the order.



    function rnatsort ( &$array = array() ) 

    {

        $keys    = array_keys($array);

        natsort($keys);

        $total    = count($keys) - 1;

        $temp1    = array();

        $temp2     = array();



        // assigning original keys to an array with a backwards set of keys, to use in krsort();

        foreach ( $keys as $key )

        {

            $temp1[$total] = $key;

            --$total;

        }

        

        ksort($temp1);



        // setting the new array, with the order from the krsort() and the values of original array.

        foreach ( $temp1 as $key ) 

        {

            $temp2[$key] = $array[$key];

        }



        $array = $temp2;

    }

@gmail bereikme
01-Sep-2006 12:06


Here's a handy function to sort an array on 1 or more columns using natural sort:

<?php

// Example: $records = columnSort($records, array('name', 'asc', 'addres', 'desc', 'city', 'asc'));



$globalMultisortVar = array();

function columnSort($recs, $cols) {

    global $globalMultisortVar;

    $globalMultisortVar = $cols;

    usort($recs, 'multiStrnatcmp');

    return($recs);

}



function multiStrnatcmp($a, $b) {

    global $globalMultisortVar;

    $cols = $globalMultisortVar;

    $i = 0;

    $result = 0;

    while ($result == 0 && $i < count($cols)) {

        $result = ($cols[$i + 1] == 'desc' ? strnatcmp($b[$cols[$i]], $a[$cols[$i]]) : $result = strnatcmp($a[$cols[$i]], $b[$cols[$i]]));

        $i+=2;

    }

    return $result;

}



?>



Greetings,



  - John

nissar_pa at yahoo dot com
04-May-2006 11:50


Here is the program which will sort an array key in natural order and maintains key to data correlations



function natSortKey(&$arrIn)

{

   $key_array = array();

   $arrOut = array();

   

   foreach ( $arrIn as $key=>$value ) {

       $key_array[]=$key;

   }

  natsort( $key_array);

  foreach ( $key_array as $key=>$value ) {

      $arrOut[$value]=$arrIn[$value];

  }

  $arrIn=$arrOut;



}



Thanks,

Abdul Nissar

12-Mar-2006 12:44


The last comment should have been posted in doc about (r)sort( ). Indeed, and unfortunately, ORDER BY *does not* perform natural ordering. So, sometimes we *must* do a SQL request followed by natsort( ).

h3
22-Feb-2006 01:59


This function can be very usefull, but in some cases, like if you want to sort a MySQL query result, it's important to keep in mind that MySQL as built'in sorting functions which are way faster than resorting the result using a complex php algorythm, especially with large arrays.



ex; 'SELECT * FROM `table` ORDER BY columnName ASC, columnName2 DESC'

lil at thedreamersmaze dot spam-me-not dot org
31-Jan-2006 01:38


There's one little thing missing in this useful bit of code posted by mbirth at webwriters dot de:



<?php



function natsort2d(&$aryInput) {

  $aryTemp = $aryOut = array();

  foreach ($aryInput as $key=>$value) {

   reset($value);

   $aryTemp[$key]=current($value);

  }

  natsort($aryTemp);

  foreach ($aryTemp as $key=>$value) {

   $aryOut[$key] = $aryInput[$key]; 

// --------^^^^ add this if you want your keys preserved!

  }

  $aryInput = $aryOut;

}



?>

natcasesort.too
05-Aug-2005 07:17


I got caught out through naive use of this feature - attempting to sort a list of image filenames from a digital camera, where the filenames are leading zero padded (e.g. DSCF0120.jpg) , will not sort correctly.

Maybe the example could be modified to exhibit this behaviour 

(e.g. set array to -img0120.jpg','IMG0.png', 'img0012.png', 'img10.png', 'img2.png', 'img1.png', 'IMG3.png)

If the example hadn't used images I would have coded it correctly first time around!

mroach at mroach dot com
28-Jun-2005 01:08


Here's an expansion of the natsort2d function that mbirth wrote. This one allows you to specify the key for sorting.



<?php

function natsort2d( &$arrIn, $index = null )

{

    

    $arrTemp = array();

    $arrOut = array();

    

    foreach ( $arrIn as $key=>$value ) {

        

        reset($value);

        $arrTemp[$key] = is_null($index)

                            ? current($value)

                            : $value[$index];

    }

    

    natsort($arrTemp);

    

    foreach ( $arrTemp as $key=>$value ) {

        $arrOut[$key] = $arrIn[$key];

    }

    

    $arrIn = $arrOut;

    

}



?>

phpnet at moritz-abraham dot de
02-Sep-2004 06:09


additional to the code posted by justin at redwiredesign dot com (which I found very usefull) here is a function that sorts complex arrays like this:

<?

$array['test0'] = array('main' =>  'a', 'sub' => 'a');

$array['test2'] = array('main' =>  'a', 'sub' => 'b');

$array['test3'] = array('main' =>  'b', 'sub' => 'c');

$array['test1'] = array('main' =>  'a', 'sub' => 'c');

$array['test4'] = array('main' =>  'b', 'sub' => 'a');

$array['test5'] = array('main' =>  'b', 'sub' => 'b');

?>

or

<?

$array[0] = array('main' =>  1, 'sub' => 1);

$array[2] = array('main' =>  1, 'sub' => 2);

$array[3] = array('main' =>  2, 'sub' => 3);

$array[1] = array('main' =>  1, 'sub' => 3);

$array[4] = array('main' =>  2, 'sub' => 1);

$array[5] = array('main' =>  2, 'sub' => 2);

?>

on one or more columns.



the code

<? $array = array_natsort_list($array,'main','sub'); ?>

will result in $array being sortet like this:

test0,test2,test1,test4,test5,test3

or

0,2,1,4,5,3.



you may even submit more values to the function as it uses a variable parameter list. the function starts sorting on the last and the goes on until the first sorting column is reached.



to me it was very usefull for sorting a menu having submenus and even sub-submenus.



i hope it might help you too.



here is the function:

<?

function array_natsort_list($array) {

    // for all arguments without the first starting at end of list

    for ($i=func_num_args();$i>1;$i--) {

        // get column to sort by

        $sort_by = func_get_arg($i-1);

        // clear arrays

        $new_array = array();

        $temporary_array = array();

        // walk through original array

        foreach($array as $original_key => $original_value) {

            // and save only values

            $temporary_array[] = $original_value[$sort_by];

        }

        // sort array on values

        natsort($temporary_array);

        // delete double values

        $temporary_array = array_unique($temporary_array);

        // walk through temporary array

        foreach($temporary_array as $temporary_value) {

            // walk through original array

            foreach($array as $original_key => $original_value) {

                // and search for entries having the right value

                if($temporary_value == $original_value[$sort_by]) {

                    // save in new array

                    $new_array[$original_key] = $original_value;

                }

            }

        }

        // update original array

        $array = $new_array;

    }

    return $array;

}

?>

xlab AT adaptiveNOSPAMarts DOT net
15-Jan-2004 05:51


Under limited testing, natsort() appears to work well for IP addresses. For my needs, it is far less code than the ip2long()/long2ip() conversion I was using before.

mbirth at webwriters dot de
09-Jan-2004 05:31


For those who want to natsort a 2d-array on the first element of each sub-array, the following few lines should do the job.



<?php



function natsort2d(&$aryInput) {

  $aryTemp = $aryOut = array();

  foreach ($aryInput as $key=>$value) {

    reset($value);

    $aryTemp[$key]=current($value);

  }

  natsort($aryTemp);

  foreach ($aryTemp as $key=>$value) {

    $aryOut[] = $aryInput[$key];

  }

  $aryInput = $aryOut;

}



?>

rasmus at flajm dot com
15-Dec-2003 02:30


To make a reverse function, you can simply:



function rnatsort(&$a){

    natsort($a);

    $a = array_reverse($a, true);

}

justin at redwiredesign dot com
22-Aug-2003 02:10


One of the things I've needed to do lately is apply natural sorting to a complex array, e.g.:



Array

(

    [0] => Array

        (

            [ID] = 4

            [name] = Fred

        )

        

    [1] => Array

        (

            [ID] = 6

            [name] = Bob

        )

)



where I want to sort the parent array by the child's name. I couldn't see a way of doing this using array_walk, so I've written a simple function to do it. Hopefully someone will find this useful:



/**

 * @return Returns the array sorted as required

 * @param $aryData Array containing data to sort

 * @param $strIndex Name of column to use as an index

 * @param $strSortBy Column to sort the array by

 * @param $strSortType String containing either asc or desc [default to asc]

 * @desc Naturally sorts an array using by the column $strSortBy

 */

function array_natsort($aryData, $strIndex, $strSortBy, $strSortType=false)

{

    //    if the parameters are invalid

    if (!is_array($aryData) || !$strIndex || !$strSortBy)

        //    return the array

        return $aryData;

        

    //    create our temporary arrays

    $arySort = $aryResult = array();

    

    //    loop through the array

    foreach ($aryData as $aryRow)

        //    set up the value in the array

        $arySort[$aryRow[$strIndex]] = $aryRow[$strSortBy];

        

    //    apply the natural sort

    natsort($arySort);



    //    if the sort type is descending

    if ($strSortType=="desc")

        //    reverse the array

        arsort($arySort);

        

    //    loop through the sorted and original data

    foreach ($arySort as $arySortKey => $arySorted)

        foreach ($aryData as $aryOriginal)

            //    if the key matches

            if ($aryOriginal[$strIndex]==$arySortKey)

                //    add it to the output array

                array_push($aryResult, $aryOriginal);



    //    return the return

    return $aryResult;

}

flash at minet dot net
12-Aug-2003 02:27


About the reverse natsort.. Maybe simpler to do :



function strrnatcmp ($a, $b) {

    return strnatcmp ($b, $a);

}

dslicer at maine dot rr dot com
02-Jun-2003 10:41


Something that should probably be documented is the fact that both natsort and natcasesort maintain the key-value associations of the array. If you natsort a numerically indexed array, a for loop will not produce the sorted order; a foreach loop, however, will produce the sorted order, but the indices won't be in numeric order. If you want natsort and natcasesort to break the key-value associations, just use array_values on the sorted array, like so:



natsort($arr);

$arr = array_values($arr);

anonymous at coward dot net
31-May-2003 05:46


Reverse Natsort:



  function rnatsort($a, $b) {

    return -1 * strnatcmp($a, $b);

  }



  usort($arr, "rnatsort");

add a note

natcasesort