$get_categories_tree = get_categories_tree();

$smarty->assign('category_1', RandArray($get_categories_tree['634'],7));
$smarty->assign('category_2', RandArray($get_categories_tree['683'],6));
$smarty->assign('category_3', RandArray($get_categories_tree['754'],4));
$smarty->assign('category_4', RandArray($get_categories_tree['837'],3));

function RandArray($arr,$num=){

    $rand_arr = array_rand($arr['cat_id'],$num);  // 随机4个类别

    foreach($rand_arr as $k=>$v){

        $f[$k] = $arr['cat_id'][$v];

    }

    return $f;

}