C# - Dictionary with Behaviour of a Ring List?

Question

I need a ring list dictionary that can store key and item. Capacity = 50 and when I add #51 the first item must be removed. Basically it must be a dictionary that behaves like a ring list.

Is there something in .NET Framework that can do that ? Or do I have to write it by myself ?

Answer 1

You won't find anything built-in I think but you can easily implement one using OrderedDictionary

OrderedDictionary maintains items in order which they are inserted. Whenever you reach the limit/capacity you can remove the first item.

Answer 2

or use an extension method :

EDIT :

because

latest added entry ends up being returned first.

so u can remove the first item like :

dictionary.Remove(dictionary.Last().Key);  

& so your extension method is :

addExtension(this Dictionary<string, object> dictionary, string key, object value)
   {
        if(dictionary.Count == 50)
                dictionary.Remove(dictionary.Last().Key);  

        dictionary.Add(key, value);   
   }

Answer 3

Try this:

class Program
{
    static void Main(string[] args)
    {
        var rD = new RingDictionary(50);
        for (int i = 0; i < 75; i++)
        {
            rD.Add(i, i);
        }
        foreach (var item in rD.Keys)
        {
            Console.WriteLine("{0} {1}", item, rD[item]);
        }
    }
}

class RingDictionary : OrderedDictionary
{
    int indexKey;

    int _capacity = 0;
    public int Capacity
    {
        get { return _capacity; }
        set
        {
            if (value <= 0)
            {
                var errorMessage = typeof(Environment)
                    .GetMethod(
                        "GetResourceString",
                        System.Reflection.BindingFlags.Static |
                        System.Reflection.BindingFlags.NonPublic,
                        null,
                        new Type[] { typeof(string) },
                        null)
                    .Invoke(null, new object[] { 
                        "ArgumentOutOfRange_NegativeCapacity" 
                    }).ToString();
                throw new ArgumentException(errorMessage);
            }
            _capacity = value;
        }
    }

    public RingDictionary(int capacity)
    {
        indexKey = -1;
        Capacity = capacity;
    }

    public new void Add(object key, object value)
    {
        indexKey++;

        if (base.Keys.Count > _capacity)
        {
            for (int i = base.Keys.Count-1; i >Capacity-1 ; i--)
            {
                base.RemoveAt(i);
            }
        }

        if (base.Keys.Count == _capacity)
        {
            base.RemoveAt(indexKey % _capacity);
            base.Insert(indexKey % _capacity, key, value);
        }
        else
        {
            base.Add(key, value);
        }
    }
}