Q:

Dictionary with multiple keys and multiple values for each key

Hi all I am having a requirement where I have to assign multiple keys and for that multiple keys I have to assign multiple values
My requirement is as follows. I am having EmpID, PayYr and PayID for each employee.
Assume I get my data as follows:
EmpID  1000    1000  1000   1000
PayYr  2011    2011  2011   2012
PayID    1      2     3      1

I would like to have my dictionary so that the dictionary with key value result is as follows:
1000 - 2011 - 1,2,3
1000 - 2012 - 1

I tried some thing as follows
public struct Tuple<T1, T2>
{
    public readonly T1 Item1;
    public readonly T2 Item2;

    public Tuple(T1 item1, T2 item2)
    {
        Item1 = item1;
        Item2 = item2;
    }
}

Sample code
for (int empcnt = 0; empcnt < iEmpID.Length; empcnt++)
    {
        for (int yrcnt = 0; yrcnt < ipayYear.Length; yrcnt++)
        {

            List<int> lst1 = new List<int>();
            var key1 = new Tuple<int, int>(iEmpID[empcnt], ipayYear[yrcnt]);
            if (!dictAddValues.ContainsKey(key1))
            {
                dictAddValues.Add(key1, lst1);
                lst1.Add(lst[yrcnt]);
            }
        }

    }

But I am not getting my result as i required so can any one help me.

A:

Personally, I'd probably use a Dictionary of Dictionaries, e.g. IDictionary<int, IDictionary<int, IList<int>>>. Not I am not entirely sure how you intend to access or facilitate this data; that will have a large impact on how efficient my suggestion is. On the upside, it would allow you to -- relatively easily -- access data, if and only if you access it in the order you set up your dictionaries.
(On second thought, simply the type declaration itself is so ugly and meaningless, you might want to skip what I said above.)
If you are accessing fields rather randomly, maybe a simple denormalized ICollection<Tuple<int, int, int>> (or equivalent) will have to do the trick, with aggregation in other parts of your application as needed. LINQ can help here a lot, especially its aggregation, grouping, and lookup features.
Update: Hopefully this clarifies it:
var outerDictionary = new Dictionary<int, Dictionary<int, List<int>>>();

/* fill initial values
 * assuming that you get your data row by row from an ADO.NET data source, EF, or something similar. */
foreach (var row in rows) {
    var employeeId = (int) row["EmpID"];
    var payYear = (int) row["PayYr"];
    var payId = (int) row["PayID"];

    Dictionary<int, int> innerDictionary;
    if (!outerDictionary.TryGet(employeeId, out innerDictionary)) {
        innerDictionary = new Dictionary<int, int>();
        outerDictionary.Add(employeeId, innerDictionary);
    }

    List<int> list;
    if (!innerDictionary.TryGet(payYear)) {
        list = new List<int>();
        innerDictionary.Add(payYear, list);
    }

    list.Add(payId);
}

/* now use it, e.g.: */
var data = outerDictionary[1000][2011]; // returns a list with { 1, 2, 3 }

Take it with a grain of salt though; see comment.

