0: 1 1: 2 2: 3 3: 5 4: 6 

Note:

Obviously in this trivial case the sort() function would be more appropriate.

 $fruits[0]: apples $fruits[1]: grapes $fruits[2]: lemons 

 b c d 

 y, a x, b z, c 

When trying to do some custom sorting with objects and an anonymous function it wasn't entirely clear how this usort function works. I think it probably uses a quicksort in the background. Basically it actually moves the $b variable up or down in respect to the $a variable. It does NOT move the $a variable inside the callback function. This is key to getting your logic right in the comparisons.

If you return -1 that moves the $b variable down the array, return 1 moves $b up the array and return 0 keeps $b in the same place.

To test I cut down my code to sorting a simple array from highest priority to lowest.

<?php
$priorities = array(5, 8, 3, 7, 3);

usort($priorities, function($a, $b)
{
    if ($a == $b)
    {
        echo "a ($a) is same priority as b ($b), keeping the same\n";
        return 0;
    }
    else if ($a > $b)
    {
        echo "a ($a) is higher priority than b ($b), moving b down array\n";
        return -1;
    }
    else {
        echo "b ($b) is higher priority than a ($a), moving b up array\n";               
        return 1;
    }
});

echo "Sorted priorities:\n";
var_dump($priorities);
?>

Output:

b (8) is higher priority than a (3), moving b up array
b (5) is higher priority than a (3), moving b up array
b (7) is higher priority than a (3), moving b up array
a (3) is same priority as b (3), keeping the same
a (8) is higher priority than b (3), moving b down array
b (8) is higher priority than a (7), moving b up array
b (8) is higher priority than a (5), moving b up array
b (8) is higher priority than a (3), moving b up array
a (5) is higher priority than b (3), moving b down array
a (7) is higher priority than b (5), moving b down array

Sorted priorities:
array(5) {
  [0]=> int(8)
  [1]=> int(7)
  [2]=> int(5)
  [3]=> int(3)
  [4]=> int(3)
}

This will sort subnets correctly:

<?php

$zones =
array('192.168.11',
'192.169.12',
'192.168.13',
'192.167.14',
'192.168.15',
'122.168.16',
'192.168.17'
);

function sort_subnets ($a, $b) {
    $a_arr = explode('.', $a);
    $b_arr = explode('.', $b);
    foreach (range(0,3) as $i) {
        if ( $a_arr[$i] < $b_arr[$i] ) {
            return -1;
        }
        elseif ( $a_arr[$i] > $b_arr[$i] ) {
            return 1;
        }
    }
    return -1;
}

usort($zones, 'sort_subnets');
print '<pre>';
print_r($zones);
print '</pre>';

?>

I wrote a wrapper for usort that lets you use something similar to an SQL ORDER BY clause. It can sort arrays of associative arrays and arrays of objects and I think it would work with some hybrid case.

Example of how the function works:

<?php
$testAry = array(
  array('a' => 1, 'b' => 2, 'c' => 3),
  array('a' => 2, 'b' => 1, 'c' => 3),
  array('a' => 3, 'b' => 2, 'c' => 1),
  array('a' => 1, 'b' => 3, 'c' => 2),
  array('a' => 2, 'b' => 3, 'c' => 1),
  array('a' => 3, 'b' => 1, 'c' => 2)
);

Utility::orderBy($testAry, 'a ASC, b DESC');

//Result:
$testAry = array(
  array('a' => 1, 'b' => 3, 'c' => 2),
  array('a' => 1, 'b' => 2, 'c' => 3),
  array('a' => 2, 'b' => 3, 'c' => 1),
  array('a' => 2, 'b' => 1, 'c' => 3),
  array('a' => 3, 'b' => 2, 'c' => 1),
  array('a' => 3, 'b' => 1, 'c' => 2)
);
?>

To sort an array of objects you would do something like:
Utility::orderBy($objectAry, 'getCreationDate() DESC, getSubOrder() ASC');

This would sort an array of objects that have methods getCreationDate() and getSubOrder().

Here is the function:

<?php
class Utility {
    /*
    * @param array $ary the array we want to sort
    * @param string $clause a string specifying how to sort the array similar to SQL ORDER BY clause
    * @param bool $ascending that default sorts fall back to when no direction is specified
    * @return null
    */
    public static function orderBy(&$ary, $clause, $ascending = true) {
        $clause = str_ireplace('order by', '', $clause);
        $clause = preg_replace('/\s+/', ' ', $clause);
        $keys = explode(',', $clause);
        $dirMap = array('desc' => 1, 'asc' => -1);
        $def = $ascending ? -1 : 1;

        $keyAry = array();
        $dirAry = array();
        foreach($keys as $key) {
            $key = explode(' ', trim($key));
            $keyAry[] = trim($key[0]);
            if(isset($key[1])) {
                $dir = strtolower(trim($key[1]));
                $dirAry[] = $dirMap[$dir] ? $dirMap[$dir] : $def;
            } else {
                $dirAry[] = $def;
            }
        }

        $fnBody = '';
        for($i = count($keyAry) - 1; $i >= 0; $i--) {
            $k = $keyAry[$i];
            $t = $dirAry[$i];
            $f = -1 * $t;
            $aStr = '$a[\''.$k.'\']';
            $bStr = '$b[\''.$k.'\']';
            if(strpos($k, '(') !== false) {
                $aStr = '$a->'.$k;
                $bStr = '$b->'.$k;
            }

            if($fnBody == '') {
                $fnBody .= "if({$aStr} == {$bStr}) { return 0; }\n";
                $fnBody .= "return ({$aStr} < {$bStr}) ? {$t} : {$f};\n";               
            } else {
                $fnBody = "if({$aStr} == {$bStr}) {\n" . $fnBody;
                $fnBody .= "}\n";
                $fnBody .= "return ({$aStr} < {$bStr}) ? {$t} : {$f};\n";
            }
        }

        if($fnBody) {
            $sortFn = create_function('$a,$b', $fnBody);
            usort($ary, $sortFn);       
        }
    }
}
?>

As the manual says, "If two members compare as equal, their order in the sorted array is undefined." This means that the sort used is not "stable" and may change the order of elements that compare equal.

Sometimes you really do need a stable sort. For example, if you sort a list by one field, then sort it again by another field, but don't want to lose the ordering from the previous field. In that case it is better to use usort with a comparison function that takes both fields into account, but if you can't do that then use the function below. It is a merge sort, which is guaranteed O(n*log(n)) complexity, which means it stays reasonably fast even when you use larger lists (unlike bubblesort and insertion sort, which are O(n^2)).

<?php
function mergesort(&$array, $cmp_function = 'strcmp') {
    // Arrays of size < 2 require no action.
    if (count($array) < 2) return;
    // Split the array in half
    $halfway = count($array) / 2;
    $array1 = array_slice($array, 0, $halfway);
    $array2 = array_slice($array, $halfway);
    // Recurse to sort the two halves
    mergesort($array1, $cmp_function);
    mergesort($array2, $cmp_function);
    // If all of $array1 is <= all of $array2, just append them.
    if (call_user_func($cmp_function, end($array1), $array2[0]) < 1) {
        $array = array_merge($array1, $array2);
        return;
    }
    // Merge the two sorted arrays into a single sorted array
    $array = array();
    $ptr1 = $ptr2 = 0;
    while ($ptr1 < count($array1) && $ptr2 < count($array2)) {
        if (call_user_func($cmp_function, $array1[$ptr1], $array2[$ptr2]) < 1) {
            $array[] = $array1[$ptr1++];
        }
        else {
            $array[] = $array2[$ptr2++];
        }
    }
    // Merge the remainder
    while ($ptr1 < count($array1)) $array[] = $array1[$ptr1++];
    while ($ptr2 < count($array2)) $array[] = $array2[$ptr2++];
    return;
}
?>

this is a new multisort function for sorting on multiple subfield like it will be in sql : 'ORDER BY field1, field2'
number of sort field is undefined
<?php

$array[] = array('soc' => 3, 'code'=>1);
$array[] = array('soc' => 2, 'code'=>1);
$array[] = array('soc' => 1, 'code'=>1);
$array[] = array('soc' => 1, 'code'=>1);
$array[] = array('soc' => 2, 'code'=>5);
$array[] = array('soc' => 1, 'code'=>2);
$array[] = array('soc' => 3, 'code'=>2);

//usage
print_r(multiSort($array, 'soc', 'code'));

function multiSort() {
    //get args of the function
    $args = func_get_args();
    $c = count($args);
    if ($c < 2) {
        return false;
    }
    //get the array to sort
    $array = array_splice($args, 0, 1);
    $array = $array[0];
    //sort with an anoymous function using args
    usort($array, function($a, $b) use($args) {

        $i = 0;
        $c = count($args);
        $cmp = 0;
        while($cmp == 0 && $i < $c)
        {
            $cmp = strcmp($a[ $args[ $i ] ], $b[ $args[ $i ] ]);
            $i++;
        }

        return $cmp;

    });

    return $array;

}
?>

output:
Array
(
    [0] => Array
        (
            [soc] => 1
            [code] => 1
        )

    [1] => Array
        (
            [soc] => 1
            [code] => 1
        )

    [2] => Array
        (
            [soc] => 1
            [code] => 2
        )

    [3] => Array
        (
            [soc] => 2
            [code] => 1
        )

    [4] => Array
        (
            [soc] => 2
            [code] => 5
        )

    [5] => Array
        (
            [soc] => 3
            [code] => 1
        )

    [6] => Array
        (
            [soc] => 3
            [code] => 2
        )

)

The easiest way to compare two integers is just to take the second away from the first. For example, say you wanted to sort by an integer property of an object. Your comparison function would look like this:

<?php
function compare_counts($a, $b) {
  return $a->count - $b->count;
}
?>

This works because you don't necessarily have to return -1, 0 or 1, the manual states any integer less than, equal to or greater than 0 is OK.

If you want to sort an array according to another array acting as a priority list, you can use this function.

<?php
function listcmp($a, $b)
{
  global $order;

  foreach($order as $key => $value)
    {
      if($a==$value)
        {
          return 0;
          break;
        }

      if($b==$value)
        {
          return 1;
          break;
        }
    }
}

$order[0] = "first";
$order[1] = "second";
$order[2] = "third";

$array[0] = "second";
$array[1] = "first";
$array[2] = "third";
$array[3] = "fourth";
$array[4] = "second";
$array[5] = "first";
$array[6] = "second";

usort($array, "listcmp");

print_r($array);
?>

sort multi-dimentional arrays in class with usort

<?php
class ArraySort
{
    private $arr = array();

    public function __construct($arr)
    {
        $this->arr = $arr;
    }

    public function doSort()
    {
        $cmp = function($a, $b)
        {
            //Do Some Comparation
        }
        if(is_array($this->arr))
        {
            usort($this->arr, $cmp);
        }
        return $this->arr;
    }
}
?>

This lets you sort an associative multi-dimensional array by multiple key/field names.  Much similiar to the SQL clause ORDER BY.  Enjoy.

<?php
function cmp ($a, $b) {

    // Populate this array with your values...
    // Below is the SQL equivalent of
    // select * from blah ORDER BY date desc, type asc, name asc

    $vals = array(
        'date' => 'd',
        'type' => 'a',
        'name' => 'a'
    );

    while(list($key, $val) = each($vals)) {

        if($val == "d") {
            if ($a["$key"] > $b["$key"]) {
                return -1;
            }
            if ($a["$key"] < $b["$key"]) {
                return 1;
            }
        }

        if($val == "a") {
            if ($a["$key"] < $b["$key"]) {
                return -1;
            }
            if($a["$key"] > $b["$key"]) {
                return 1;
            }
        }

    }

}
?>

For using usort inside a method in an object, where the callback sort method is in the same object, this works:

<?php usort($arr_to_sort, array($this, "sort_terms_by_criteria")); ?>

If you wish to keep elements in their original or reverse order if they are the same length, just don't return zero for items that compare the same. Return a 1 or -1, as appropriate.

This function will sort on more then one values, test and have fun

<pre>
<?php

  $array[0]['name'] = "a";
  $array[0]['id'] = 3;

  $array[1]['name'] = "a";
  $array[1]['id'] = 2;

  $array[2]['name'] = "a";
  $array[2]['id'] = 5;

  $array[3]['name'] = "b";
  $array[3]['id'] = 8;

  $array[4]['name'] = "b";
  $array[4]['id'] = 1;

  $array[5]['name'] = "b";
  $array[5]['id'] = 0;

  $array[6]['name'] = "c";
  $array[6]['id'] = 5;

  $array[7]['name'] = "c";
  $array[7]['id'] = 7;

  $array[8]['name'] = "c";
  $array[8]['id'] = 3;

  print_r($array);

  $sort_array[0]['name'] = "name";
  $sort_array[0]['sort'] = "ASC";
  $sort_array[0]['case'] = TRUE;

  $sort_array[1]['name'] = "id";
  $sort_array[1]['case'] = FALSE;

  sortx($array, $sort_array);

  print_r($array);

  function sortx(&$array, $sort = array()) {
    $function = '';
    while (list($key) = each($sort)) {
      if (isset($sort[$key]['case'])&&($sort[$key]['case'] == TRUE)) {
        $function .= 'if (strtolower($a["' . $sort[$key]['name'] . '"])<>strtolower($b["' . $sort[$key]['name'] . '"])) { return (strtolower($a["' . $sort[$key]['name'] . '"]) ';
      } else {
        $function .= 'if ($a["' . $sort[$key]['name'] . '"]<>$b["' . $sort[$key]['name'] . '"]) { return ($a["' . $sort[$key]['name'] . '"] ';
      }
      if (isset($sort[$key]['sort'])&&($sort[$key]['sort'] == "DESC")) {
        $function .= '<';
      } else {
        $function .= '>';
      }
      if (isset($sort[$key]['case'])&&($sort[$key]['case'] == TRUE)) {
        $function .= ' strtolower($b["' . $sort[$key]['name'] . '"])) ? 1 : -1; } else';
      } else {
        $function .= ' $b["' . $sort[$key]['name'] . '"]) ? 1 : -1; } else';
      }
    }
    $function .= ' { return 0; }';
    usort($array, create_function('$a, $b', $function));
  }

?>
</pre>

I needed a sort method that would sort strings but take note of any numbers and would compare them as number. I also want to ignore any non alphanumerical characters.

Eg.
Slot 1 Example
Slot 10 Example
Slot 2 Example

Should infact be
Slot 1 Example
Slot 2 Example
Slot 10 Example

<?php
function sort_with_numbers($a , $b) {
    $a = explode(' ',$a);
    $b = explode(' ',$b);
    $size = min(count($a), count($b));
    for($index =0; $index < $size; ++$index) {
        $a1 = ereg_replace("[^A-Za-z0-9]", "",$a[$index]);
        $b1 = ereg_replace("[^A-Za-z0-9]", "",$b[$index]);
        $equal = 0;
        if (is_numeric($a1) && is_numeric($b1)) {
            $equal = $a1 - $b1;
        } else {
            $equal = strcasecmp($a1,$b1);
        }
        if ($equal < 0) {
            return -1;
        }
        if ($equal > 0) {
            return 1;
        }
    }
    return count($a) - count($b);   
}
?>

An even better implementation of osort [than my original, posted on 24-AUG-09 (since deleted)], allowing for multiple properties and directions.  With php 5.3.0 sorting by properties of an object becomes MUCH simpler.  Note that this uses anonymous functions / closures. Might find reviewing the php docs on that useful.  Look below for examples for previous version of php.

<?php
function osort(&$array, $props)
{
    if(!is_array($props))
        $props = array($props => true);
       
    usort($array, function($a, $b) use ($props) {
        foreach($props as $prop => $ascending)
        {
            if($a->$prop != $b->$prop)
            {
                if($ascending)
                    return $a->$prop > $b->$prop ? 1 : -1;
                else
                    return $b->$prop > $a->$prop ? 1 : -1;
            }
        }
        return -1; //if all props equal       
    });   
}
?>

Usage:

<?php
osort($items, array("Color" => true, "Size" => false));
//or
osort($items, "Color");
?>

If you need to use usort with a key in the calling method, I wrote this as a utility:
<?php

function usort_comparison($obj, $method, $key) {
    $usorter = &new Usort($obj, $method, $key);
    return array($usorter, "sort");
}

class Usort {
    function __construct($obj, $method, $key) {
        $this->obj = $obj;
        $this->method = $method;
        $this->key = $key;
    }
    function sort($a, $b) {
        return call_user_func_array(array($this->obj, $this->method), array($a, $b, $this->key));
    }
}

?>

<?php

require_once("util/usort.php");

class Foo {
    $items = array(FooBar(13), FooBar(2));
    public function sorter() {
        usort($this-items, usort_comparison("Foo", "_cmp", "item"));
    }

    public static function _cmp($a, $b, $key) {
         return strcasecmp($a->$key, $b->$key);
    }

}

class FooBar {
    public $item;
    function __construct($val) {
        $this->item = $val;
    }
}

?>

~ simple example... but in the way I need to use it was the key was used in a switch statement to choose the different member of the object to compare against dynamically (as in, sort by x or y or z)

<?php
/*---------------------------------------------------------
* my own home made easy object sort, which
* i cannot find anywhere on the net
* at all, tut. i can find only complicated ones,
* which brings me a headache.
*
* You can enhance it to return all sorts of error
* conditions if you wish,
* i need nothing but a false return upon failure to sort,
* so that is the only error i have here
*
* Example usage:
*
* INPUT                 -       $objects_array
// an array of objects for sorting

* PARAMETERS    -       property
// the property of the object to be sorted

* OUTPUT                -       $engine
// an engine object created by new,
// with your arrays of objects sorted according to your
// selected property
//( the sorting is done upon sort object creation )
*
* Code Examples
*
* $engine = new objSorter($objects_array);
// sorts on FIRST property -  default

* $engine = new objSorter($objects_array,'property');
// sort on ANY specific property
*--------------------------------------------------------*/

class objSorter
{
var $property;
var $sorted;

    function ObjSorter($objects_array,$property=null)
        {
            $sample    = $objects_array[0];
            $vars    = get_object_vars($sample);

        if (isset($property))
            {
            if (isset($sample->$property))
// make sure requested property is correct for the object
                {   
                $this->property = $property;
                usort($objects_array, array($this,'_compare'));
                }
            else
                {   
                $this->sorted    = false;
                return;   
                }
            }
        else
            {   
                list($property,$var)     = each($sample);
                $this->property         = $property;
                usort($objects_array, array($this,'_compare'));
            }

        $this->sorted    = ($objects_array);
        }

    function _compare($apple, $orange)
        {
        $property    = $this->property;
        if ($apple->$property == $orange->$property) return 0;
        return ($apple->$property < $orange->$property) ? -1 : 1;
        }
} // end class
?>

USAGE EXAMPLE
DUMP ORIGINAL
user Object ( [name] => Yunihe Jopoba [age] => 27 [richness] => € 899,970 )
user Object ( [name] => Janirevi Fakejorumoa [age] => 19 [richness] => € 219,078 )
user Object ( [name] => Korejowi Mezede [age] => 95 [richness] => € 3,272 )
user Object ( [name] => Nugoaivu Jongyi [age] => 84 [richness] => € 94,853 )
user Object ( [name] => Cepomase Buaesukoyua [age] => 32 [richness] => € 677,180 )
user Object ( [name] => Vejosehona Auva [age] => 20 [richness] => € 144,540 )
user Object ( [name] => Fewame Wojuvuzo [age] => 69 [richness] => € 198,231 )
user Object ( [name] => Risuku Zagedobu [age] => 48 [richness] => € 763,860 )
user Object ( [name] => Fazurada Aayu [age] => 16 [richness] => € 302,352 )

SORTED by age

<?php
$objects                = new ObjSorter($objects_array,'age');
if ($objects->sorted)
{
$objects_array  = $objects->sorted;
foreach ($objects_array as $key=>$object) { print_r($object); echo "<br />"; }
}
?>

user Object ( [name] => Fazurada Aayu [age] => 16 [richness] => € 302,352 )
user Object ( [name] => Janirevi Fakejorumoa [age] => 19 [richness] => € 219,078 )
user Object ( [name] => Vejosehona Auva [age] => 20 [richness] => € 144,540 )
user Object ( [name] => Yunihe Jopoba [age] => 27 [richness] => € 899,970 )
user Object ( [name] => Cepomase Buaesukoyua [age] => 32 [richness] => € 677,180 )
user Object ( [name] => Risuku Zagedobu [age] => 48 [richness] => € 763,860 )
user Object ( [name] => Fewame Wojuvuzo [age] => 69 [richness] => € 198,231 )
user Object ( [name] => Nugoaivu Jongyi [age] => 84 [richness] => € 94,853 )
user Object ( [name] => Korejowi Mezede [age] => 95 [richness] => € 3,272 )

SORTED by richness

<?php
$objects                = new ObjSorter($objects_array,'richness');
if ($objects->sorted)
{
$objects_array  = $objects->sorted;
foreach ($objects_array as $key=>$object) { print_r($object); echo "<br />"; }
}
?>

user Object ( [name] => Vejosehona Auva [age] => 20 [richness] => € 144,540 )
user Object ( [name] => Fewame Wojuvuzo [age] => 69 [richness] => € 198,231 )
user Object ( [name] => Janirevi Fakejorumoa [age] => 19 [richness] => € 219,078 )
user Object ( [name] => Korejowi Mezede [age] => 95 [richness] => € 3,272 )
user Object ( [name] => Fazurada Aayu [age] => 16 [richness] => € 302,352 )
user Object ( [name] => Cepomase Buaesukoyua [age] => 32 [richness] => € 677,180 )
user Object ( [name] => Risuku Zagedobu [age] => 48 [richness] => € 763,860 )
user Object ( [name] => Yunihe Jopoba [age] => 27 [richness] => € 899,970 )
user Object ( [name] => Nugoaivu Jongyi [age] => 84 [richness] => € 94,853 )

Simulated wrong property request ( dumb property )

<?php
$objects                = new ObjSorter($objects_array,'dumb property');
if ($objects->sorted)
{
$objects_array  = $objects->sorted;
foreach ($objects_array as $key=>$object) { print_r($object); echo "<br />"; }
}
else echo 'DUMB ERROR';
?>

DUMB ERROR

Here's how you can usort() a multidimensional array (like in example #2 above) within a class:

<?php usort($myArray, array("className", "cmp")); ?>

Sorting a multidimensional array by a subkey seem to be one of the bigger challenges when using usort. At least if one want the key to be dynamic. For anyone interested this code seemed to work rather well for me:

<?php

usort($array,array(new cmp($key), "cmp__"));

class cmp {
    var $key;
    function __construct($key) {
        $this->key = $key;
    }
   
    function cmp__($a,$b) {
        $key = $this->key;
        if ($a[$key] == $b[$key]) return 0;
        return (($a[$key] > $b[$key]) ? 1 : -1);
    }
}

?>

here's another recursive multisort, however a clean and fast one that is class-based (but works as well outside classes) and does not uglify your global namespace at all. note that strnatcmp is used, but one could use something else of course.

btw, for arrays in which the rows/columns are 'swapped', use array_multisort().

<?php
class Banana {
    var $aData;//the array we want to sort.
    var $aSortkeys;//the order in which we want the array to be sorted.
    function _sortcmp($a, $b, $i=0) {
        $r = strnatcmp($a[$this->aSortkeys[$i]],$b[$this->aSortkeys[$i]]);
        if($r==0) {
            $i++;
            if ($this->aSortkeys[$i]) $r = $this->_sortcmp($a, $b, $i+1);
        }
        return $r;
    }
    function sort() {
        if(count($this->aSortkeys)) {
            usort($this->aData,array($this,"_sortcmp"));
        }
    }
}
$B = new Banana;
$B->aData = array(
    array("name" => "hank", "headsize" => "big", "age" => 32),
    array("name" => "frank", "headsize" => "huge", "age" => 36)
);
$B->aSortkeys = array("age","name");
$B->sort();

?>
sorry for the ugly indenting, but i couldn't get it any better in this note adder thing.

Here is a simple example of converting a timestamp date("U") into a date. This sorts by that day and then by string value alphabetically.

I hope it saves someone some time... Happy PHP'in!

<?php
//data to sort
$shared[0]["page_id"] = "2025731470";
$shared[1]["page_id"] = "2025731450";
$shared[2]["page_id"] = "1025731456";
$shared[3]["page_id"] = "1025731460";
$shared[0]["username"] = "larry";
$shared[1]["username"] = "alvin";
$shared[2]["username"] = "garth";
$shared[3]["username"] = "harvy";

//function to convert timestamp to date
function convert_timestamp($timestamp){
    $limit=date("U");
    $limiting=$timestamp-$limit;
    return date ("Ymd", mktime (0,0,$limiting));
}
//comparison function
function cmp ($a, $b) {
    $l=convert_timestamp($a["page_id"]);
    $k=convert_timestamp($b["page_id"]);
    if($k==$l){
        return strcmp($a["username"], $b["username"]);
    }else{
        return strcmp($k, $l);
    }
}

//sort array
usort($shared, "cmp");

//display sorted info
while (list ($key, $value) = each ($shared)) {
    echo "\$shared[$key]: ";
    echo $value["page_id"];
    echo " username: ";
    echo $value["username"];
    echo "<break_tag>";
}
?>

This will output:
$shared[0]: 2025731450   username: alvin
$shared[1]: 2025731470   username: larry
$shared[2]: 1025731456   username: garth
$shared[3]: 1025731460   username: harvy

I'd like to share with the community my function for sorting an array of arrays or objects containing associative data. This could be used, for example, with a MySQL result.

<?php
function sort_by($field, &$arr, $sorting=SORT_ASC, $case_insensitive=true){
    if(is_array($arr) && (count($arr)>0) && ( ( is_array($arr[0]) && isset($arr[0][$field]) ) || ( is_object($arr[0]) && isset($arr[0]->$field) ) ) ){
        if($case_insensitive==true) $strcmp_fn = "strnatcasecmp";
        else $strcmp_fn = "strnatcmp";

        if($sorting==SORT_ASC){
            $fn = create_function('$a,$b', '
                if(is_object($a) && is_object($b)){
                    return '.$strcmp_fn.'($a->'.$field.', $b->'.$field.');
                }else if(is_array($a) && is_array($b)){
                    return '.$strcmp_fn.'($a["'.$field.'"], $b["'.$field.'"]);
                }else return 0;
            ');
        }else{
            $fn = create_function('$a,$b', '
                if(is_object($a) && is_object($b)){
                    return '.$strcmp_fn.'($b->'.$field.', $a->'.$field.');
                }else if(is_array($a) && is_array($b)){
                    return '.$strcmp_fn.'($b["'.$field.'"], $a["'.$field.'"]);
                }else return 0;
            ');
        }
        usort($arr, $fn);
        return true;
    }else{
        return false;
    }
}
?>

To sort reliably on more than one "column" in database-style arrays, handle this within your cmp function where the first field to be sorted returns 0:

<?php

function cmp($a, $b){
   
if($a[field_1] == $b[field_1]){

  if($a[field_2] == $b[field_2]){

   return 0;

  }

  elseif($a[field_2] > $b[field_2]){

   return -1;

  }

  elseif($a[field_2] < $b[field_2]){

   return 1;

  }

}

elseif($a[field_1] > $b[field_1]){

  return -1;

}

elseif($a[field_1] < $b[field_1]){

  return 1;

}

}

?>

Sorting by doing multiple passes does not seem to be reliable.

Needed a quick, fairly uncluttered way of sorting an array of objects by a certain object attribute, so here's what I came up with. Uses one global array and usort(). Also accepts an optional sort direction argument (CSORT_ASC = sort ascending, CSORT_DESC = sort descending). Use it like this:

(assuming $myarray is your array, "index" is the attribute you want to sort by, and you want to sort in descending order)

      csort($myarray, "index", CSORT_DESC);

Hope this is of use to someone. Probably a better way to pull this off, but this works alright.

<?php
define("CSORT_ASC",     1);
define("CSORT_DESC",     -1);

function csort_cmp(&$a, &$b)
{
    global $csort_cmp;

    if ($a->$csort_cmp['key'] > $b->$csort_cmp['key'])
        return $csort_cmp['direction'];

    if ($a->$csort_cmp['key'] < $b->$csort_cmp['key'])
        return -1 * $csort_cmp['direction'];

    return 0;
}

function csort(&$a, $k, $sort_direction=CSORT_ASC)
{
    global $csort_cmp;

    $csort_cmp = array(
        'key'           => $k,
        'direction'     => $sort_direction
    );

    usort($a, "csort_cmp");

    unset($csort_cmp);
}
?>

You can also sort multi-dimensional array for multiple values like as

<?php
$arr = [
    [
        "name"=> "Sally",
        "nick_name"=> "sal",
        "availability"=> "0",
        "is_fav"=> "0"
    ],
    [
        "name"=> "David",
        "nick_name"=> "dav07",
        "availability"=> "0",
        "is_fav"=> "1"
    ],
    [
        "name"=> "Zen",
        "nick_name"=> "zen",
        "availability"=> "1",
        "is_fav"=> "0"
    ],
    [
        "name"=> "Jackson",
        "nick_name"=> "jack",
        "availability"=> "1",
        "is_fav"=> "1"
    ],
    [
        "name"=> "Rohit",
        "nick_name"=> "rod",
        "availability"=> "0",
        "is_fav"=> "0"
    ],

];

usort($arr,function($a,$b){
    $c = $b['is_fav'] - $a['is_fav'];
    $c .= $b['availability'] - $a['availability'];
    $c .= strcmp($a['nick_name'],$b['nick_name']);
    return $c;
});

print_r($arr);
?>

Output:

Array
(
    [0] => Array
        (
            [name] => Jackson
            [nick_name] => jack
            [availability] => 1
            [is_fav] => 1
        )

    [1] => Array
        (
            [name] => David
            [nick_name] => dav07
            [availability] => 0
            [is_fav] => 1
        )

    [2] => Array
        (
            [name] => Zen
            [nick_name] => zen
            [availability] => 1
            [is_fav] => 0
        )

    [3] => Array
        (
            [name] => Rohit
            [nick_name] => rod
            [availability] => 0
            [is_fav] => 0
        )

    [4] => Array
        (
            [name] => Sally
            [nick_name] => sal
            [availability] => 0
            [is_fav] => 0
        )

)

As the documentation says, the comparison function needs to return an integer that is either "less than, equal to, or greater than zero". There is no requirement to restrict the value returned to -1, 0, 1.

<?php
usort($array, function($a, $b) {
    if($a->integer_property > $b->integer_property) {
        return 1;
    }
    elseif($a->integer_property < $b->integer_property) {
        return -1;
    }
    else {
        return 0;
    }
});
?>

can be simplified to

<?php
usort($array, function($a, $b) {
    return $a->integer_property - $b->integer_property;
});
?>

This of course applies to any comparison function that calculates an integer "score" for each of its arguments to decide which is "greater".

Below is a variation on Example #4 that implements a multi-key natural sort on an associative array and can be called in such a way as to allow reversing the sort order and/or making the comparison case insensitive on a key by key basis.

Test code is included in the file – run it from the command line with: php sortUtils.php

<?php
/**
*    sortUtils.php
*/

/**
*    mknatsort() - Multi-Key Natural Sort for associative arrays
*
*    Uses the usort() function to perform a natural sort on a multi-dimensional
*    array on multiple keys. Optionally specifying the sort order for each key
*    and/or ignoring the case for each key value.
*
*    @param array $data_array The array to be sorted.
*    @param mixed $keys The list of keys to be sorted by. This may be a single
*        key or an array of keys
*    @param boolean $reverse Specify whether or not to reverse the sort order. If
*        there are multiple keys then $reverse may be an array of booleans - one
*        per key.
*    @param boolean $ignorecase Specify whether or not to ignore the case when
*        comparing key values.reverse the sort order. If there are multiple keys
*        then $ignorecase may be an array of booleans - one per key.
*/
function mknatsort ( &$data_array, $keys, $reverse=false, $ignorecase=false ) {
    // make sure $keys is an array
    if (!is_array($keys)) $keys = array($keys);
    usort($data_array, sortcompare($keys, $reverse, $ignorecase) );
}

function sortcompare($keys, $reverse=false, $ignorecase=false) {
    return function ($a, $b) use ($keys, $reverse, $ignorecase) {
        $cnt=0;
        // check each key in the order specified
        foreach ( $keys as $key ) {
            // check the value for ignorecase and do natural compare accordingly
            $ignore = is_array($ignorecase) ? $ignorecase[$cnt] : $ignorecase;
            $result = $ignore ? strnatcasecmp ($a[$key], $b[$key]) : strnatcmp($a[$key], $b[$key]);
            // check the value for reverse and reverse the sort order accordingly
            $revcmp = is_array($reverse) ? $reverse[$cnt] : $reverse;
            $result = $revcmp ? ($result * -1) : $result;
            // the first key that results in a non-zero comparison determines
            // the order of the elements
            if ( $result != 0 ) break;
            $cnt++;
        }
        return $result;
    };
} // end sortcompare()

// test code that will be skipped if this is included in the web environment
// test with: php sortUtils.php from the command line
$sapi_type = php_sapi_name();
if (substr($sapi_type, 0, 3) == 'cli') {

    // the following shows several examples of usage and the resulting output.
    $test[] = array('Status'=>'In Progress', 'comment'=>'This looks good.', 'user_name'=>'John Doe', 'date_modified'=>'06/13/2014 11:20 AM', 'role'=>'Senior Account Manager');
    $test[] = array('Status'=>'In Progress', 'comment'=>'This looks good, please approve.', 'user_name'=>'John Doe', 'date_modified'=>'06/13/2014 11:19 AM', 'role'=>'Account Manager');
    $test[] = array('Status'=>'In Progress', 'comment'=>'This looks good.', 'user_name'=>'Jane Smith', 'date_modified'=>'06/13/2014 11:19 AM', 'role'=>'Senior Account Manager');
    $test[] = array('Status'=>'Returned', 'comment'=>'There is not enough informartion.  Please add the following.', 'user_name'=>'John Doe', 'date_modified'=>'06/13/2014 11:15 AM', 'role'=>'Account Manager');
    $test[] = array('Status'=>'In Progress', 'comment'=>'I am currently reviewing this.', 'user_name'=>'John Doe', 'date_modified'=>'06/13/2014 11:14 AM', 'role'=>'Account Manager');
    echo "Original array: ";
    print_r($test);

    echo "Sorted on date_modified: ";
    mknatsort($test, array('date_modified') );
    print_r($test);

    echo "Sorted on role(reversed) & date_modified: ";
    mknatsort($test, array('role','date_modified'),array(true,false) );
    print_r($test);

    echo "Sorted on role & date_modified(reversed): ";
    mknatsort($test, array('role','date_modified'),array(false,true) );
    print_r($test);
}

?>

This comment is just to help backward compatibility.

I needed to have a foreach loop using reference just before using the usort function on the same array that was used in the foreach.

Like this:
<?php
public function sortByTitle()
{
        if(empty($this->_arrSubCat))
            return false;
       
        foreach($this->_arrSubCat as &$cat)
            $cat->sortByTitle();
       
        usort($this->_arrSubCat, 'strcasecmp');
}
?>

I had this strange bug where the last object of the $this->_arrSubCat array before the sort was alway replaced/overwrited with his string value.

On my machine (PHP 5.3), I had no problem, but when I placed the code on another server, my code crashed with a fatal error (Because I was using a string as an object later in the code)

The solution I found is really simple, and avoid the array to have a reference declared in memory while running the sort function. Just add an unset($cat):

<?php
public function sortByTitle()
{
        if(empty($this->_arrSubCat))
            return false;
       
        foreach($this->_arrSubCat as &$cat)
            $cat->sortByTitle();
       
        unset($cat); //No more problem because of the foreach &cat reference.   
        usort($this->_arrSubCat, 'strcasecmp');
}
?>

It took me an hour an a half to locate the bug, hope it will save someone some time !

If you ever have to sort a collection of objects on something like a string (name) present in every object, but want to keep the array of objects intact you might find this useful:

<?php
function naturalSortObjectArray($objectArray) {
        function naturalSortByName($a, $b) {
            return strnatcmp($a->name, $b->name);
        }
        usort($objectArray, "naturalSortByName");
        return $objectArray;
}
?>

Remember that functions inside of functions will become part of the global scope too. So, something like:

<?php
    function foo($array) {
        function compare($a,$b) {
            return $a < $b;
        }
        usort($array, "compare");
        return $array;
    }
   
    function bar($array) {
        function compare($a,$b) {
            return $a > $b;
        }
        usort($array, "compare");
        return $array;
    }
   
    foo($something);
    bar($something_else);
?>
       
Will result in a fatal error because you're redeclaring 'compare'. This could be a little strange, e.g. for JavaScript programmers who expect functions in functions to become private outside of the parent scope.

I see many people here (including the official examples) write their callbacks rather clumsily like this:

<?php
function($a, $b) {
  if ($a === $b) {
    return 0;
  } elseif ($a < $b) {
    return -1; 
  } else {
    return 1;
  }
}
?>

Or if they are a bit more clever:

<?php
function($a, $b) {

  if ($a === $b) {
    return 0;
  } else {
    return $a < $b ? -1 : 1;
  }
}
?>

But this can by simplified further to:

<?php
function($a, $b) {
  return $a - $b;
}
?>

Here's how to use usort() within a class using a static function as a callback (using the example above):

<?php

class MyObj {
    var $name;

    function SampleObj($name){
        $this->name = $name;

        usort($this->name, array(&$this, "compareValues"));

    }

    static function compareValues($a, $b){
        $al = strtolower($a->name);
        $bl = strtolower($b->name);
        if ($al == $bl) {
            return 0;
        }
        return ($al > $bl) ? +1 : -1;
    }
}

?>

<?php
/**
* Sort array of objects by field.
*
* @param array $objects Array of objects to sort.
* @param string $on Name of field.
* @param string $order (ASC|DESC)
*/
function sort_on_field(&$objects, $on, $order = 'ASC') {
    $comparer = ($order === 'DESC')
        ? "return -strcmp(\$a->{$on},\$b->{$on});"
        : "return strcmp(\$a->{$on},\$b->{$on});";
    usort($objects, create_function('$a,$b', $comparer));
}
?>

strcmp (or strcasecmp) can be used as a callback function for usort. It will cast your comparison values to string. Thus, you can implement a __toString() method into your classes and use usort without creating a callback function:

<?php
class Foo {
   private $a;
   private $b;

   public function __construct($a, $b) {
      $this->a = $a;
      $this->b = $b;
   }

   public function __toString() {
      return (string)$this->a;
   }
}

$foo = array(new Foo('t', 'b'), new Foo('a', 'c'), new Foo('g', 'd'));

print_r($foo);

usort($foo, 'strcasecmp');

print_r($foo);
?>

Needed to sort an array of objects based on multiple properties. (ie: Group, then Last Name, then First Name) Doing this in multiple usorts fails because the second usort ends up shuffling the results of the previous usort because order is undefined when criteria are equal. Ended up writing a function that builds a comparison operator by nesting ternary operators for each field, then using that function in usort(). Hopefully it's of use to someone else.

<?php
/*
* Sorts an array of objects by a list of properties.
* Each property can have the following options:
*   'property' can be either a public variable or a method().
*   'order' can be ASC or DESC
*   'comparer' can be string, number, or date
*
* Example:
* sortObjectsByProperties($objects, array(
*       array('property'=>'getPrice()', order=>'ASC', 'comparer'=>'number'),
*       array('property'=>'getName()', order=>'DESC', 'comparer'=>'string'),
*       array('property'=>'created_date', order=>'ASC', 'comparer'=>'date'),
*       array('property'=>'id', order=>'ASC', 'comparer'=>'number'),
*   ));
*
* @author Tyler Chamberlain
*/
function sortObjectsByProperties(&$objects, $fields) {
        $comparerFunctionString = "";
        foreach ($fields as $field) {
            if ($field['comparer'] == 'number') {
                $comparerFunction = "(\$a->{$field['property']} == \$b->{$field['property']} ? 0 : (\$a->{$field['property']} > \$b->{$field['property']} ? 1 : -1))";
            } elseif ($field['comparer'] == 'date') {
                $comparerFunction = "(strtotime(\$a->{$field['property']}) > strtotime(\$b->{$field['property']}) ? 1 : -1)";
            } else {
                $comparerFunction = "strcasecmp(\$a->{$field['property']},\$b->{$field['property']})";
            }
            if ($field['order'] === 'DESC') { $comparerFunction = "-".$comparerFunction; }
            $comparerFunctionString .= "$comparerFunction != 0 ? $comparerFunction : (";
        }
        $comparer = "return ($comparerFunctionString 0 )".str_repeat(")", sizeof($fields)).";";
        usort($objects, create_function('$a,$b', $comparer));
}
?>

In order to get a proper text sorting I have changed the arfsort() function submitted by jonathan(at)inetz(dot)com.

The one line I have changed is:

<?php
$strc = strcmp( $a[$f], $b[$f] );
?>

to

<?php
$strc = strcmp( strtolower($a[$f]), strtolower($b[$f]) );
?>

It can now sort correctly for alphabetization.  Capital letters where getting in the way.

Sean

When I query a DB I usually put my record set inside of a multi-dimentional array.  I finally wrote a program that will allow you to sort your record set by column after you put it in an array.

<?php
$test = array();
$test[0]['name'] = 'jeremy';
$test[0]['email'] = 'lala@example.com';
$test[0]['phone'] = '123-123-1234';
$test[0]['trick'] = 'mezopia';

$test[1]['name'] = 'Amanda';
$test[1]['email'] = 'hot@example.com';
$test[1]['phone'] = '123-123-1235';
$test[1]['trick'] = 'youarecool';

$test[2]['name'] = 'john';
$test[2]['email'] = 'wowee@example.com';
$test[2]['phone'] = '123-123-3333';
$test[2]['trick'] = 'goneinanhour';

print_r(columnSort($test, 'name'));

function columnSort($unsorted, $column) {
    $sorted = $unsorted;
    for ($i=0; $i < sizeof($sorted)-1; $i++) {
      for ($j=0; $j<sizeof($sorted)-1-$i; $j++)
        if ($sorted[$j][$column] > $sorted[$j+1][$column]) {
          $tmp = $sorted[$j];
          $sorted[$j] = $sorted[$j+1];
          $sorted[$j+1] = $tmp;
      }
    }
    return $sorted;
}
?>

Now, in php 7, we can use the spaceship operator. For example lest sort array of words from element string length:

<?php
$sampleArray = ['one', 'two', free', 'fore', 'five'];

usort($sampleArray, function($a, $b) {
      return strlen($a) <=> strlen($b);
});

The usort function actually moves $b up when the callback function returns both 0 and 1.  If you want to preserve the original order in the array, return 1 when $a == $b instead of 0.  Try this code below to see how usort alters the order of the original array when all values are the same.

<?php
class TestObj {
    private $name;
    private $id;

    function TestObj($name, $id) {
        $this->name = $name;
        $this->id = $id;
    }

    static function cmp_obj($a, $b) {
        $al = strtolower($a->name);
        $bl = strtolower($b->name);
        if ($al == $bl) {
            return 0; // return 1 if you don't want $b to go in front of $a
        }
        return ($al > $bl) ? +1 : -1;
    }
}

$a[] = new TestObj("a", 1);
$a[] = new TestObj("a", 2);
$a[] = new TestObj("a", 3);

var_dump($a);
usort($a, array("TestObj", "cmp_obj"));
var_dump($a);
?>

The array_alternate_multisort function written by robert below doesn't work. There are several bugs in the code and it doesn't work when sorting by multiple keys because the order of the first key isn't taken into account when sorting by the second key and so on. Also, because robert uses strcasecmp the algorithm doesn't work properly with floats or other variable types. Here's the improved version:

<?php
    function SortArray() {
        $arguments = func_get_args();
        $array = $arguments[0];
        $code = '';
        for ($c = 1; $c < count($arguments); $c += 2) {
            if (in_array($arguments[$c + 1], array("ASC", "DESC"))) {
                $code .= 'if ($a["'.$arguments[$c].'"] != $b["'.$arguments[$c].'"]) {';
                if ($arguments[$c + 1] == "ASC") {
                    $code .= 'return ($a["'.$arguments[$c].'"] < $b["'.$arguments[$c].'"] ? -1 : 1); }';
                }
                else {
                    $code .= 'return ($a["'.$arguments[$c].'"] < $b["'.$arguments[$c].'"] ? 1 : -1); }';
                }
            }
        }
        $code .= 'return 0;';
        $compare = create_function('$a,$b', $code);
        usort($array, $compare);
        return $array;
    }
?>

If you want to sort an array of strings by the length of its values, you can write a better cmp-function than manually comparing string lengths with if-statements. Unfortunately, I see this bad technique in other people's code. I prefer using this:

<?php
function length_cmp( $a, $b ) {
    return strlen($a)-strlen($b) ;
}
?>

This function sorts the array in ascending order. If you want to sort descending, simply swap $a and $b either in the parameters or in the subtraction.

-Tim

Another way to compare object is to have a compare static function in the class with reccursion ability and have globals or static variables who save the state of comparison, and the order.

It could be a good idea to have a variable with comparison functions name (with the sorting : numeric, alphanumeric, inverse).

<?php
interface Comparable{static function compare($a, $b);}
class myObj implements Comparable{
        var $var1; var $var2; var $var3;
        function __construct($v1, $v2, $v3){
                $this->var1=$v1; $this->var2=$v2; $this->var3=$v3;
        }
        public function __toString() {
                return "v1 ".$this->var1." v2 ".$this->var2." v3 ".$this->var3;
        }
        static function compare($a, $b){
                $sort=$GLOBALS['sorts'][$GLOBALS['sort']];
                echo "$sort\n";
                if($a->$sort == $b->$sort){
                        if($GLOBALS['sorts'][$GLOBALS['sort']+1]){
                                $GLOBALS['sort']++;
                                $res=  call_user_func(array('myObj', 'compare'), $a, $b);
                                $GLOBALS['sort']=0; return $res;
                        }
                        $GLOBALS['sort']=0; return 0;
                }
                $GLOBALS['sort']=0;
                if($a->$sort > $b->$sort)
                        return 1;
                return -1;
        }
}

$objects = array(new myObj("1", "2", "3"), new myObj("2", "2", "2"), new myObj("1", "3", "4"));

/* Tests */
$sorts=Array('var1', 'var2', 'var3'); $sort = 0; usort($objects, array('myObj', 'compare')); echo ("var1 var2 var3\n"); foreach($objects as $o)echo $o."\n";
$sorts=Array('var2', 'var3', 'var1'); $sort = 0; usort($objects, array('myObj', 'compare')); echo ("\nvar2 var3 var1\n"); foreach($objects as $o)echo $o."\n";
$sorts=Array('var2', 'var1', 'var3'); $sort = 0; usort($objects, array('myObj', 'compare')); echo ("\nvar2 var1 var3\n"); foreach($objects as $o)echo $o."\n";

?>

Instead of doing  :

<?php $strc = strcmp( strtolower($a[$f]), strtolower($b[$f]) ); ?>

you could do this :

<?php $strc = strcasecmp( $a[$f], $b[$f] ); ?>

which is more efficient and is does case insensitive comparison according to the current locale.

For sort multi-array by specific index

<?php
function cmp ($a, $b)
{  
global $w_o;
if ($a[$w_o] == $b[$w_o]) return 0;
return ($a[$w_o] < $b[$w_o]) ? -1 : 1;
}
# the index is the second element of
# each row

$w_o =1;
usort($my_arry_info,"cmp");
?>

Needed a date sort and I didn't know if one was available so I wrote one. Maybe it'll help someone:

<?php
function DateSort($a,$b,$d="-") {
    if ($a == $b) {
        return 0;
    } else {  //Convert into dates and compare
        list($am,$ad,$ay)=split($d,$a);
        list($bm,$bd,$by)=split($d,$b);
        if (mktime(0,0,0,$am,$ad,$ay) < mktime(0,0,0,$bm,$bd,$by)) {
            return -1;
        } else {
            return 1;
        }
    }
}
?>

$d is the delimeter

If you've used ADO before, you may have used the Sort property on a recordset.  It's very powerful - you can add a nice ORDER BY clause after getting the recordset from the database.  It's especially helpful if you want to show a list on a web page and make the column headings links that cause the list to resort on that column.

I wanted to do the same thing with mysql recordsets, but it looks like you have to have the ORDER BY in your query.  I re-worked the example from johan_land at yahoo dot com above for sorting multidimensional arrays.  When I get a mysql recordset, I create an array with all of the records like this:

<?php
$aaRows[]    = array();
if (mysql_num_rows($rsRows) > 0)
    while ($aRow = mysql_fetch_array($rsRows, MYSQL_ASSOC))
        $aaRows[]    = $aRow;
?>

At this point $aaRows is an array of arrays - it's a numeric-indexed array containing records from the recordset, which themselves are associative arrays.  The following code takes the array of records as the first parameter, and an array of fields to sort - each field is an associative array, where 'name' is the db field name, and 'dir' is the direction to sort.  If dir is 'DESC' (case-insensitive), it will sort descending.  Any other value (including not setting one) will cause it to sort ascending.

<?php
function sortRows(&$a_aaRows, $a_aaSortCriteria)
{
    GLOBAL    $g_aaSortArray;

    function compare($a_aRow1, $a_aRow2, $a_lField = 0)
    {
        GLOBAL    $g_aaSortArray;

        $lCompareVal    = 0;

        if ($a_lField < count($g_aaSortArray))
        {
            $sSortFieldName    = $g_aaSortArray[$a_lField]['name'];
            $sSortFieldDir    = $g_aaSortArray[$a_lField]['dir'];

            $vValue1    = eval('return $a_aRow1[' . $sSortFieldName . '];');
            $vValue2    = eval('return $a_aRow2[' . $sSortFieldName . '];');

            if ($vValue1 == $vValue2)
                $lCompareVal    = compare($a_aRow1, $a_aRow2, $a_lField + 1);
            else
            {
                $lCompareVal    =    $vValue1 > $vValue2 ? 1 : -1;
                if (strtolower(substr($sSortFieldDir, 0, 4)) == 'desc')
                    $lCompareVal    = -$lCompareVal;
            }
        }

        return $lCompareVal;
    }

    $g_aaSortArray    = $a_aaSortCriteria;
    usort($a_aaRows, 'compare');
}
?>

When I call it it looks something like this:

<?php
sortRows($aaRows, array(array('name' => 'STATE', 'dir' => 'ASC'), array('name' => 'CITY', 'dir' => 'DESC')));
?>