Warning: array_multisort() [function.array-multisort]: Argument #1 is expected to be an array or a sort flag in

function array_multisort_by_order(array $array, $by, array $order)
{
     $max = max(array_map('count',$array));
    //or, alternatively, depending on input (if there are no 'complete' subarrays):
    //$max = max(array_map(function($arr){return max(array_keys($arr));},$array))+1;

    //ADDITION: negative numeric keys:
    $min = min(array_map(function($arr){return min(array_keys($arr));},$array));
    $width = $max - min(0,$min);

    foreach($array as &$sub){
        // $addin = array_diff_key(array_fill(0,$max,null),$sub);
        // $addin changed for negative keys:
        $addin = array_diff_key(array_combine(range($min,$max),array_fill(0,$width,null)),$sub);
        $sub = $addin + $sub;
        ksort($sub);
    }
    $order = array_flip($order);
    $params[] = $array[$by];
    foreach($params[0] as &$v) $v = $order[$v];
    foreach($array as &$v) $params[] = &$v; unset($v);
    call_user_func_array('array_multisort', $params);
    //no closeures here:
    //foreach($array as &$sub) $sub = array_filter(function($a){return !is_null($a);},$sub);
    $filter = create_function('$a','return !is_null($a);');
    foreach($array as &$sub) $sub = array_filter($sub,$filter);
    return $array;
}

<?
$data['test1'] = array('volume' => 67, 'edition' => 2, 'name' => 6, 'type' => 2);
$data['test2'] = array('volume' => 86, 'edition' => 1, 'name' => 7, 'type' => 2);
$data['test3'] = array('volume' => 85, 'edition' => 6, 'name' => 8, 'type' => 2);
$data['test4'] = array('volume' => 98, 'edition' => 2, 'name' => 9, 'type' => 2);
$data['test5'] = array('volume' => 86, 'edition' => 6, 'name' => 10, 'type' => 2);
$data['test6'] = array('volume' => 67, 'edition' => 7, 'name' => 11, 'type' => 2);

//Create index rows
foreach ($data as $row) {
  foreach ($row as $key => $value){
    ${$key}[]  = $value; //Creates $volume, $edition, $name and $type arrays.
  }  
}

//ex: sort by edition asc, then by name DESC:

array_multisort($edition, SORT_ASC, $name, SORT_DESC, $data);

echo "<pre>";
print_r($data);
echo "</pre>";
?>

Array
(
    [test2] => Array
        (
            [volume] => 86
            [edition] => 1
            [name] => 7
            [type] => 2
        )

    [test4] => Array
        (
            [volume] => 98
            [edition] => 2
            [name] => 9
            [type] => 2
        )

    [test1] => Array
        (
            [volume] => 67
            [edition] => 2
            [name] => 6
            [type] => 2
        )

    [test5] => Array
        (
            [volume] => 86
            [edition] => 6
            [name] => 10
            [type] => 2
        )

    [test3] => Array
        (
            [volume] => 85
            [edition] => 6
            [name] => 8
            [type] => 2
        )

    [test6] => Array
        (
            [volume] => 67
            [edition] => 7
            [name] => 11
            [type] => 2
        )

)

$letters = array("b","a","c");
$numbers = array(5,4,2);

$letters = array("b","a","a");
$numbers = array(5,4,2);

$items = array("a","b","z","a","z","z");

uasort($items, "sortByPredefinedOrder");

function sortByPredefinedOrder($leftItem, $rightItem){
  $order = array("a","z","b","x"); //defined somewhere

  $flipped = array_flip($order); //so we can access "position by value"

  $leftPos = $flipped[$leftItem];
  $rightPos = $flipped[$rightItem];
  return $leftPos >= $rightPos;   
}

print_r($items); //Array ( [0] => a [3] => a [2] => z [4] => z [5] => z [1] => b )

  $leftPos = $flipped[$leftItem["volume"]];
  $rightPos = $flipped[$rightItem["volume"]];

// Input arrays
$ar[1] = array("game", "scissors", "rock", "paper");
$ar[2] = array("D", "B", "A", "C");
$ar[3] = array("four", "two", "one", "three");

// Build the list of arguments for array_multisort()
// Use references to the arrays you want it to sort
$supar = array(&$ar[2], &$ar[1], &$ar[3]);

// Call array_multisort() indirectly
// This is the same as array_multisort($ar[2], $ar[1], $ar[3]);
call_user_func_array('array_multisort', $supar);

$cats=[
    ["category_code"=>"BB","category"=>"","item_count"=>"1","max_qty"=>12000], 
    ["category_code"=>"AK","category"=>"Anklet","item_count"=>"1","max_qty"=>6], 
    ["category_code"=>"BAC","category"=>"Bag Accessories","item_count"=>"2","max_qty"=>352],
    ["category_code"=>"WB","category"=>"Bags","item_count"=>"9","max_qty"=>6290], 
    ["category_code"=>"AB","category"=>"Bathroom Accessories","item_count"=>"19","max_qty"=>325],
    ["category_code"=>"BK","category"=>"Book","item_count"=>"40","max_qty"=>27291]
];

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

var_export($cats);

array (
  0 => 
  array (
    'category_code' => 'BK',
    'category' => 'Book',
    'item_count' => '40',
    'max_qty' => 27291,
  ),
  1 => 
  array (
    'category_code' => 'BB',
    'category' => '',
    'item_count' => '1',
    'max_qty' => 12000,
  ),
  2 => 
  array (
    'category_code' => 'WB',
    'category' => 'Bags',
    'item_count' => '9',
    'max_qty' => 6290,
  ),
  3 => 
  array (
    'category_code' => 'BAC',
    'category' => 'Bag Accessories',
    'item_count' => '2',
    'max_qty' => 352,
  ),
  4 => 
  array (
    'category_code' => 'AB',
    'category' => 'Bathroom Accessories',
    'item_count' => '19',
    'max_qty' => 325,
  ),
  5 => 
  array (
    'category_code' => 'AK',
    'category' => 'Anklet',
    'item_count' => '1',
    'max_qty' => 6,
  ),
)