>>>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.....