SingleOrDefault() when the sequence contains the default value

Question

I have stumbled upon an interesting scenario, which I couldn't find a solution to. Suppose I have to find the majorant in a sequence (the number that occurs at least n / 2 + 1 times, where n is the size of the sequence). This is my implementation:

public static int FindMajorant(IList<int> numbers)
{
    return numbers
        .GroupBy(x => x)
        .Where(g => g.Count() >= numbers.Count / 2 + 1)
        .Select(g => g.Key)
        .SingleOrDefault();
}

I'm using SingleOrDefault(), which returns the element if it's found in the sequence or the default value for the type: in this case, it will return 0 as it's the default value for an int. For example, my method returns 3 for the following sequence:

List<int> sampleNumbers = new List<int>() { 2, 2, 3, 3, 2, 3, 4, 3, 3 };

which is the expected behaviour.

However, what happens if the majorant in the sequence is zero (0)? It would return 0, but that way, how could I determine whether it's the zero from SingleOrDefault() as a default value, or the majorant? Perhaps, I could use Single(), but that would throw an exception which is pretty much incorrent. I could also catch this exception, but this seems a bad practice to me. So my question is, what's the preferred way to handle this situation?

Answer 1

Use a nullable value where null indicates that there is no majorant, rather than using "0" to mean that. And conveniently enough, the default value of int? is null, so the only change needed to your code is to get a sequence of nullable ints before calling SingleOrDefault.

public static int? FindMajorant(IList<int> numbers)
{
    return numbers
        .GroupBy(x => x)
        .Where(g => g.Count() >= numbers.Count / 2 + 1)
        .Select(g => (int?)g.Key)
        .SingleOrDefault();
}