How to group friends by the first letter of the last name in UItableView into sections

I have friend struct model.

struct Friend {
    let name: String
    let photoImageName: String
}

And my FriendsViewController with tableview outlet

final class FriendsViewController: UIViewController {
    // MARK: - IBOutlet

    @IBOutlet var tableView: UITableView!
    
    // MARK: - Private Properties

    private var friendsArray = [
        Friend(name: "Donald Trump", photoImageName: "donald"),
        Friend(name: "Mister Alan", photoImageName: "alan"),
        Friend(name: "Eric Cartman", photoImageName: "cartman"),
        Friend(name: "Tom Cruze", photoImageName: "cruze"),
    ]

    // MARK: - Lifecycle

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
        configureTable()
    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "GoToDetailPhoto" {
            guard let destVC = segue.destination as? DetailPhotoCollectionViewController else { return }
            if let indexPath = tableView.indexPathForSelectedRow {
                let imageToTransfer = friendsArray[indexPath.row].photoImageName
                destVC.imageName = imageToTransfer
            }
        }
    }

    // MARK: - Private methods

    private func configureTable() {
        tableView.dataSource = self
        friendsArray.sort { $0.name < $1.name }
    }
}

// MARK: - Table view data source

extension FriendsViewController: UITableViewDataSource {
    func numberOfSections(in tableView: UITableView) -> Int {
        1
    }

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        friendsArray.count
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        guard let cell = tableView.dequeueReusableCell(
            withIdentifier: FriendViewCell.identifier,
            for: indexPath
        ) as? FriendViewCell else { return UITableViewCell() }
        cell.configure(friend: friendsArray[indexPath.row])
        return cell
    }
}

How to separate them into different sections by first letter of lastname. Like in contacts app. Thank you for you answers. I think about dictionary with character but cant write it correctly

Changed array to two demensional array :

private var friendsArray = [
        [Friend(name: "Donald Trump", photoImageName: "donald")],
        [Friend(name: "Mister Alan", photoImageName: "alan")],
        [Friend(name: "Eric Cartman", photoImageName: "cartman"),
        Friend(name: "Tom Cruze", photoImageName: "cruze")],
    ]

func numberOfSections(in tableView: UITableView) -> Int {
        filteredArrayOfGroups.count
    }
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        filteredArrayOfGroups[section].count
    }

func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
        let label = UILabel()
        label.text = friendsArray[section][0].name.first?.description ?? ""
        label.backgroundColor = UIColor.white.withAlphaComponent(0.5)
        return label
    }