read csv file most booked rooms

Question

I've got a project resit from university to get done, its basically to return a bunch of things from a CSV file in java.

I've managed to do most of it from my previous attempt but one part I'm stuck on is how to read a CSV file but only a particular part of the file: the room with the most booked time and for it to be displayed in the terminal when jmh is run and made a new jar file. my first attempt was hard-coding and although it works it's not what the lecturer wanted. any help or directional pointers would be great code bellow is the way the lecturer didn't want it.

Also, the format of the CSV file is A) id B) room name C) date D) time E) length of booking F) person booking

public String[] getTopRoomsBooked(int n) {

    HashMap<String, Integer> rooms = new HashMap<String, Integer>();

    rooms.put("Gower", 281);
    rooms.put("Usk", 291);
    rooms.put("Wye", 283);
    rooms.put("Bala", 282);
    rooms.put("Pen y Fan", 292);
    rooms.put("Llangorse", 290);
    rooms.put("Snowdon", 288);
    rooms.put("Taff", 296);
    rooms.put("Cadair Idris", 292);

    for (String i : rooms.keySet()) {
        System.out.println("Room name: " + i + " Amount of time: " + rooms.get(i));
    }

    System.out.println();

    List<Integer> timeBooked = new ArrayList<>(rooms.values());

    Collections.sort(timeBooked, Collections.reverseOrder());

    if (n == 1) {
        System.out.println("RoomName : Taff " + timeBooked.get(n - 1));
    } else if (n == 3) {
        System.out.println("1: Taff " + timeBooked.get(n - 3));
        System.out.println("2: Cadiar Idris " + timeBooked.get(n - 2));
        System.out.println("3: Pen y Fan " + timeBooked.get(n - 1));

    } else if (n == 5) {
        System.out.println("1: Taff " + timeBooked.get(n - 5));
        System.out.println("2: Cadair Idris " + timeBooked.get(n - 4));
        System.out.println("3: Pen y Fan " + timeBooked.get(n - 3));
        System.out.println("4: Usk " + timeBooked.get(n - 2));
        System.out.println("5: Llangorse " + timeBooked.get(n - 1));
    } else if (n == 9) {
        System.out.println("1: Taff " + timeBooked.get(n - 9));
        System.out.println("2: Cadair Idris " + timeBooked.get(n - 8));
        System.out.println("3: Pen y Fan " + timeBooked.get(n - 7));
        System.out.println("4: Usk " + timeBooked.get(n - 6));
        System.out.println("5: Llangorse " + timeBooked.get(n - 5));
        System.out.println("6: Snowden " + timeBooked.get(n - 4));
        System.out.println("7: Wye " + timeBooked.get(n - 3));
        System.out.println("8: Bala " + timeBooked.get(n - 2));
        System.out.println("9: Gower " + timeBooked.get(n - 1));
    }

    return null;

}

Answer 1

This can be implemented using Java 8 streams using the following features:

• Comparator.comparing(...).thenComparing() to sort stream of Map.Entry<String, Integer> by the booked time value in reverse order, then by the room name
• limit the amount of output
• map remap to room name (key in rooms hashmap)
• collect(Collectors.toList()).toArray(String[]::new) collect room names to String array

Assuming that the rooms hashmap is populated outside the method getTopRoomsBooked and is provided as an argument, let's rewrite it as follows:

public static String[] getTopRoomsBooked(Map<String, Integer> rooms, int n) {

    // just for the row id in inner print
    AtomicInteger id = new AtomicInteger(1);
  
    Comparator<Map.Entry<String, Integer>> byTime = Comparator.comparing(Map.Entry::getValue, Comparator.reverseOrder());
    Comparator<Map.Entry<String, Integer>> byName = Comparator.comparing(Map.Entry::getKey);
    
    return rooms.entrySet().stream()
                .sorted(byTime.thenComparing(byName))
                .limit(n)
    // inner print       
                .peek(e -> System.out.printf("%d: %s %d%n", id.getAndIncrement(), e.getKey(), e.getValue())) 
                .map(Map.Entry::getKey)
                .collect(Collectors.toList())
                .toArray(String[]::new);
}

Test & Output

    int[] arr = {1, 3, 5};
    Arrays.stream(arr)
          .forEach(a -> System.out.println("Top " + a + ":\n" 
              + Arrays.toString(Main.getTopRoomsBooked(rooms, a)) 
              + "\n======\n"
    ));
//////////////////////////////////////////////////////////////////

1: Taff 296
Top 1:
[Taff]
======

1: Taff 296
2: Cadair Idris 292
3: Pen y Fan 292
Top 3:
[Taff, Cadair Idris, Pen y Fan]
======

1: Taff 296
2: Cadair Idris 292
3: Pen y Fan 292
4: Usk 291
5: Llangorse 290
Top 5:
[Taff, Cadair Idris, Pen y Fan, Usk, Llangorse]
======

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