>>>>>Using a Dictionary < Tkey, TValue > would be better
>>>>
>>>>Thanks, I remember having read some of that in previous threads. I might have to consider that.
>>>
>>>
>>>You can update the value of a dictionary
>>>
>>>Here, I use a Tuple of three integers - for simplicity the first one is the key
>>>
>>>
>>>

>>>		public static void Main()
>>>		{
>>>
>>>
>>>			Dictionary<int, Tuple<int, int, int>> dict = new Dictionary<int, Tuple<int, int, int>>();
>>>
>>>			Tuple<int, int, int> t;  // key is tuple.Item1
>>>
>>>			t = new Tuple<int, int, int>(1, 1, 1);
>>>			UpdateDictionary(dict, t);
>>>
>>>			t = new Tuple<int, int, int>(2, 1, 1);
>>>			UpdateDictionary(dict, t);
>>>
>>>			PrintDictionary("Before any update", dict);
>>>
>>>			t = new Tuple<int, int, int>(2, 2, 2);
>>>			UpdateDictionary(dict, t);
>>>
>>>			PrintDictionary("After update", dict);
>>>			Console.ReadLine();
>>>		}
>>>		static void UpdateDictionary(Dictionary<int, Tuple<int, int, int>> dict, Tuple<int, int, int> t)
>>>		{
>>>			if (dict.ContainsKey(t.Item1) )
>>>			{
>>>				dict[t.Item1] = t;
>>>			}
>>>			else
>>>				dict.Add(t.Item1, t);
>>>		}
>>>		static void PrintDictionary(string msg, Dictionary<int, Tuple<int, int, int>> dict)
>>>		{
>>>			Console.WriteLine(msg);
>>>			foreach (KeyValuePair<int, Tuple<int, int, int>> x in dict)
>>>			{
>>>				Console.WriteLine("{0} {1} {2}", x.Value.Item1, x.Value.Item2, x.Value.Item3);
>>>			}
>>>
>>>		}
>>>

Since the key is in the data I'd consider using KeyedCollection instead of Dictionary ?
>>UPDATE : Assuming the key is an int.....
>
>Well - I made the key part of the data for simplicity - it doesn't need to be
>
>If you go for a KeyedCollection, wouldn't you need to subclass KeyedCollection first (and implement GetKeyForItem() ? http://msdn.microsoft.com/en-us/library/ms132454.aspx)

Yes. Maybe not worth the candle but would be simpler when adding items etc......