public class Bag<T> : IVisitableCollection<T>, IBag<T>
{
      // Methods      
      public void Accept(IVisitor<KeyValuePair<T, int>> visitor);      
      public void Add(T item, int amount);      
      public Bag<T> Difference(Bag<T> bag);
      public IEnumerator<KeyValuePair<T, int>> GetCountEnumerator();
      public IEnumerator<T> GetEnumerator();
      public Bag<T> Intersection(Bag<T> bag);
      public bool IsEqual(Bag<T> bag);
      public static Bag<T> operator +(Bag<T> b1, Bag<T> b2);
      public static Bag<T> operator *(Bag<T> b1, Bag<T> b2);
      public static Bag<T> operator -(Bag<T> b1, Bag<T> b2);      
      public bool Remove(T item, int max);            
      public Bag<T> Union(Bag<T> bag);
      // ...


      // Properties      
      public int this[T item] { get; }
      // ....     
} 

A Bag is a data structure containing any amount of elements. It differs from a set in that it allows multiple instances of items to be contained in the collection, and is thus more geared towards "counting" items. The Bag data structure contained in this library is implemented by using a Dictionary{<T, int> data structure, keeping a reference to the number of items contained in the Bag.

The Bag class is implemented using a Dictionary<KeyType, int> object where the object gets hashed with a counter representing the amount of specific items contained in the Bag. The standard operations are implemented:

• Intersection - Returns a Bag containing items contained in both Bags.
• Union - Returns a Bag with all the items in both Bags.
• Difference - "Subtract" one Bag from another. This operation subtracts the number of items contained in the other Bag on the applied Bag.