SetBuilder Class

public Set RandomSample(Set set, int returnCount)
{
    //Return the original set if there are fewer tuples
    //in the set than the number requested.
    if (set.Tuples.Count <= returnCount)
        return set;

    System.Random r = new System.Random();
    SetBuilder returnSet = new SetBuilder();

    //Retrieve random tuples until the return set is filled.
    int i = set.Tuples.Count;
    foreach (Tuple t in set.Tuples)
    {
        if (r.Next(i) < returnCount)
        {
            returnCount--;
            returnSet.Add(t);
        }
        i--;
        //Stop the loop if we have enough tuples.
        if (returnCount == 0)
            break;
    }
    return returnSet.ToSet();
}