Question

I am currently developing a program that uses C#’s Dictionary container (specifically, SortedDictionary). This container works very well for my purposes except for one specific case because I want random access. Specifically, I am generating a random position using a pseudorandom number generator and I need to be able to access that value in the SortedDictionary. At the point that this happens, I do not have a key value.

I could potentially switch to a List which would solve this problem, but would create problems in the rest of the algorithm where SortedDictionary works quite well. Any suggestions/solutions would be much appreciated.

I am currently developing Visual Studio 2005.

Thank you.

Answer 1

    public TValue GetRandomElement<TKey, TValue>(SortedDictionary<TKey, TValue> dict)
    {
        Random randGen = new Random();
        int randIndex = randGen.Next(dict.Values.Count);
        int i = 0;
        foreach (TValue value in dict.Values)
        {
            if (i++ == randIndex)
                return value;
        }

        // this shouldn't happen unless I have a bug above or you are accessing the dictionary from multiple threads
        return default(TValue);
    }

Blindly enumerating the ValueCollection is not the most efficient thing in the world. But it gets the job done. If this is a frequent operation in your scenario, you should consider a hybrid data structure that has the performance characteristics needed for both dictionary lookup and random access.