There's no need to include your own API code to natsort an associative array by key.  PHP's in-built functions (other than natsort) can do the job just fine:

<?php
  uksort($myArray, "strnatcmp");
?>

Be careful of the new behaviour in 5.2.10 version.
See the following sample:

<?php

$array = array('1 bis', '10 ter', '0 PHP', '0', '01', '01 Ver', '0 ', '1 ', '1');

natsort($array);
echo '<pre>';
print_r($array);
echo '</pre>';
?>

5.2.6-1 will output:
Array
(
    [3] => 0
    [6] => 0 
    [2] => 0 OP
    [4] => 01
    [5] => 01 Ver
    [8] => 1
    [7] => 1 
    [0] => 1 bis
    [1] => 10 ter
)

5.2.10 will output:
Array
(
    [6] => 0 
    [3] => 0
    [8] => 1
    [4] => 01
    [7] => 1 
    [5] => 01 Ver
    [0] => 1 bis
    [1] => 10 ter
    [2] => 0 OP
)

Greetings

About the reverse natsort.. Maybe simpler to do :

function strrnatcmp ($a, $b) {
    return strnatcmp ($b, $a);
}

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!

Reverse Natsort:

  function rnatsort($a, $b) {
    return -1 * strnatcmp($a, $b);
  }

  usort($arr, "rnatsort");

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.

To make a reverse function, you can simply:

function rnatsort(&$a){
    natsort($a);
    $a = array_reverse($a, true);
}

Note: negatives number.
<?php
$a = array(-5,-2,3,9);
natsort($a);
print_r($a);
?>
Will output:
Array ( [1] => -2 [0] => -5 [2] => 3 [3] => 9 )

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;
}

?>

This made me waste a lot of my precious youth ... natsort() is buggy if all numbers don't have the same number of decimal places.

(php 5.6.4-4ubuntu6.2)

<?php 
$different_decimal_places_in_values = array('D'=>'13.59', '14.6' => '14.6', 'C-' => '14.19'); 
natsort($a); 
var_dump($a);

/*echoes
array(3) {
  'D' =>
  string(5) "13.59"
  '14.6' =>
  string(4) "14.6" <----------- badly ordered
  'C-' =>
  string(5) "14.19"
}*/
?>

While this 

<?php 
$same_num_decimal_places_in_values = array('D'=>'13.59', '14.6' => '14.60', 'C-' => '14.19'); natsort($a); var_dump($a);

/*echoes 
array(3) {
  'D' =>
  string(5) "13.59"
  'C-' =>
  string(5) "14.19"
  '14.6' =>
  string(5) "14.60" <--------- that is the correct position
}
*/

?>

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;
    }

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'

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;
}
?>

$array1 = $array2 = array('IMG0.png', 'img12.png', 'img10.png', 'img2.png', 'img1.png', 'IMG3.png');

natsort($array1);
echo "\n natsort(); \n";
print_r($array1);

sort($array2, SORT_NATURAL);
echo "\n sort() with  SORT_NATURAL Option\n";
print_r($array2);

Ouput:

natsort();
Array
(
    [0] => IMG0.png
    [5] => IMG3.png
    [4] => img1.png
    [3] => img2.png
    [2] => img10.png
    [1] => img12.png
)

sort() with  SORT_NATURAL Option
Array
(
    [0] => IMG0.png
    [1] => IMG3.png
    [2] => img1.png
    [3] => img2.png
    [4] => img10.png
    [5] => img12.png
)

as we can see it's  the same values but not the same keys, and also it's same for sort($array1, SORT_NATURAL | SORT_FLAG_CASE); and natcasesort($array2)

To naturally sort by array key, the uksort function can be used.

<?php

echo "Sort by keys\n";
$smoothie = array('orange' => 1, 'apple' => 1, 'yogurt' => 4, 'banana' => 4);
print_r($smoothie);
uksort( $smoothie, 'strnatcmp');
print_r($smoothie)

?>

Output:

Sort by keys
Array
(
    [orange] => 1
    [apple]  => 1
    [yogurt] => 4
    [banana] => 4
)
Array
(
    [apple]  => 1
    [banana] => 4
    [orange] => 1
    [yogurt] => 4
)

See http://php.net/manual/en/function.uksort.php for more information about uksort and http://php.net/strnatcmp for usage of strnatcmp.

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

natsort might not act like you would expect with zero padding, heres a quick sample.

<?php
$array = array('09', '8', '10', '009', '011');
natsort($array);
?>
/*
Array
(
    [3] => 009
    [4] => 011
    [0] => 09
    [1] => 8
    [2] => 10
)
*/

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;
}

?>

As noted in other notes, natsort() does _not_ always return the expected sort order. It seems especially buggy when decimals or 0 padding is used. I've filed this bug report on the issue:
https://bugs.php.net/bug.php?id=74672