C# Sorted List by Value with Object

Question

I\'m trying to create an \"ordered\" cache of objects in C#, where the order is determined by how many times that has been accessed.

I\'ve looked into Dictionary, Sorted

Answer 1

Wonder if you are after something like this.

You could store two sets of relationships; all the objects, by key to make retrieval fast, and all of the objects by Hits to store the ordering. This has the added advantage of speeding up access - you can get the Result, the Hits, and therefore it's current and next index quite quickly.

When Getting a result, we lock the access to ensure we change it's order atomically, then return the object. We also cheat when writing out the number of hits; we know what the most popular is and then we can just walk backwards through that collection - could really even extract the keys to a List, sort it, then iterate through that.

public class PopularityContest{

    private Dictionary> PopularityContainer { get; set; }

    private Dictionary ResultContainer { get; set; }

    private int MaxPopularity = 0;

    public PopularityContest(){
        PopularityContainer = new Dictionary>();
        ResultContainer = new Dictionary();
    }

    private Object _SyncLock = new Object();

    public Result GetResult(string resultKey)
    {

      Result result = ResultContainer[resultKey];

      lock(_SyncLock)
      {

        int currentHits = result.Hits;

        if(PopularityContainer.ContainsKey(currentHits) && PopularityContainer[currentHits].Contains(result))
        {
           PopularityContainer[currentHits].Remove(result);
        }

        if(!PopularityContainer.ContainsKey(currentHits + 1))
        {
          PopularityContainer.Add(currentHits + 1, new List());
        }

        PopularityContainer[currentHits + 1].Add(Result);

        if((currentHits + 1) > MaxPopularity) { MaxPopularity = currentHits + 1;}

      }

      return result;

    }


    public void WritePopularity()
    {

      //Here could also extract the keys to a List, sort it, and walk that.
      //Note, as this is a read operation, dependent upon ordering, you would also consider locking here.

      for(int i = MaxPopularity; i >= 0; i--)
      {
         if(PopularityContainer.Contains(i) && PopularityContainer[i].Count > 0)
         {
            //NB the order of items at key[i] is the order in which they achieved their popularity
            foreach(Result result in PopularityContainer[i])
            {
            Console.WriteLine(String.Format("{0} has had {1} hits", result.ToString(), i));
            }
         }

      }
    }

}