Question

I need a Dictionary like object that can store multiple entries with the same key. Is this avaliable as a standard collection, or do I need to roll my own?

To clarify, I want to be able to do something like this:

var dict = new Dictionary<int, String>();
dict.Add(1, "first");
dict.Add(1, "second");

foreach(string x in dict[1])
{
    Console.WriteLine(x);
}

Output:

first
second

Answer 1

In .NET 3.5 you can use a Lookup instead of a Dictionary.

var items = new List<KeyValuePair<int, String>>();
items.Add(new KeyValuePair<int, String>(1, "first"));
items.Add(new KeyValuePair<int, String>(1, "second"));
var lookup = items.ToLookup(kvp => kvp.Key, kvp => kvp.Value);

foreach (string x in lookup[1])
{
    Console.WriteLine(x);
}

The Lookup class is immutable. If you want a mutable version you can use EditableLookup from MiscUtil.