Multi Value Dictionary?

Question

Anyone know of a good implementation of a MultiValueDictionary? Basically, I want something that allows multiple values per key. I want to be able to do somethi

Answer 1

Just to add my $0.02 to the collection of solutions:

I had the same need back in 2011 and created a MultiDictionary with a pedantically complete implementation of all the .NET interfaces. That includes enumerators that return a standard KeyValuePair and support for the IDictionary.Values property providing a collection of actual values (instead of an ICollection>).

That way, it fits in neatly with the rest of the .NET collection classes. I also defined an IMultiDictionary interface to access operations that are particular to this kind of dictionary:

public interface IMultiDictionary :
  IDictionary>,
  IDictionary,
  ICollection>,
  IEnumerable>,
  IEnumerable {

  /// 
Adds a value into the dictionary
  /// Key the value will be stored under
  /// Value that will be stored under the key
  void Add(TKey key, TValue value);

  /// 
Determines the number of values stored under a key
  /// Key whose values will be counted
  /// The number of values stored under the specified key
  int CountValues(TKey key);

  /// 

  ///   Removes the item with the specified key and value from the dictionary
  /// 
  /// Key of the item that will be removed
  /// Value of the item that will be removed
  /// True if the item was found and removed
  bool Remove(TKey key, TValue value);

  /// 
Removes all items of a key from the dictionary
  /// Key of the items that will be removed
  /// The number of items that have been removed
  int RemoveKey(TKey key);

}

It can be compiled on anything from .NET 2.0 upwards and so far I've deployed it on the Xbox 360, Windows Phone 7, Linux and Unity 3D. There's also a complete unit test suite covering every single line of the code.

The code is licensed under the Common Public License (short: anything goes, but bug fixes to the library's code have to published) and can be found in my Subversion repository.