check for duplicates in arraylist

Question

I have an arraylist that contains items called Room. Each Room has a roomtype such as kitchen, reception etc. I want to check the arraylist to see if any rooms of that type exist before adding it to the list. Can anyone recommend a neat way of doing this without the need for multiple foreach loops?

(.NET 2.0)

Cheers

Answer 1

if (!rooms.Any (r => r.RoomType == typeToFind /*kitchen, ...*/))
  //add it or whatever

Answer 2

I would not use ArrayList here; since you have .NET 2.0, use List<T> and all becomes simple:

List<Room> rooms = ...
string roomType = "lounge";
bool exists = rooms.Exists(delegate(Room room) { return room.Type == roomType; });

Or with C# 3.0 (still targetting .NET 2.0)

bool exists = rooms.Exists(room => room.Type == roomType);

Or with C# 3.0 and either LINQBridge or .NET 3.5:

bool exists = rooms.Any(room => room.Type == roomType);

(the Any usage will work with more types, not just List<T>)

Answer 3

I havent got access to the linq technology as am running on .net 2.0. I should have stated that in the question. Apologies

Answer 4

Without using lambda expressions:

void AddRoom(Room r, IList<Room> rooms, IDictionary<string, bool> roomTypes)
{
   if (!roomTypes.Contains(r.RoomType))
   {
      rooms.Add(r);
      roomTypes.Add(r.RoomType, true);
   }
}

It doesn't actually matter what the type of the value in the dictionary is, because the only thing you're ever looking at is the keys.

Answer 5

Another way is to sort the array, then walk the elements until you find a pair of adjacent duplicates. Make it to the end, and the array is dupe-free.

Answer 6

From your question it's not 100% clear to me if you want to enforce the rule that there may be only one room of a given type, or if you simply want to know.

If you have the invariant that no collection of Rooms may have more than one of the same Room type, you might try using a Dictionary<Type, Room>.

This has the benefit of not performing a linear search on add.

You would add a room using the following operations:

if(rooms.ContainsKey(room.GetType()))
{
   // Can't add a second room of the same type
   ...
}
else
{
   rooms.Add(room.GetType(), room);
}