$model1 = new stdClass();
$model1->id = 1;
$model1->category = "cat1";
$model2 = new stdClass();
$model2->id = 2;
$model1->category = "cat2";

$models = array($model1, $model2);

$container = new \Sortable\Container($models);

$container->sortBy('id','down');


foreach($container as $item){
   echo $item->id;
}

$container = new \Sortable\Container($models);
$container->limit(1);

foreach($container as $item){
   echo $item->id;
}

$container = new \Sortable\Container($models);
$container->groupBy('category');

foreach($container as $category => $items){
   echo $category;
   $items->limit(1);
   foreach($items as $item){
       echo $item->id;
   }
}