How can I set a UITableView to grouped style

If i understand what you mean, you have to initialize your controller with that style. Something like:

myTVContoller = [[UITableViewController alloc] initWithStyle:UITableViewStyleGrouped];

You can do the following:

UITableView *myTable = [[UITableView alloc] initWithFrame:CGRectZero style:UITableViewStyleGrouped];

Swift 3:

let tableView = UITableView.init(frame: CGRect.zero, style: .grouped)