How to check if all list items have the same value and return it, or return an “otherValue” if they don’t?

Question

If all the items in a list have the same value, then I need to use that value, otherwise I need to use an “otherValue”. I can’t think of a simple and clear way of doing this

Answer 1

This may be late, but an extension that works for value and reference types alike based on Eric's answer:

public static partial class Extensions
{
    public static Nullable Unanimous(this IEnumerable> sequence, Nullable other, IEqualityComparer comparer = null)  where T : struct, IComparable
    {
        object first = null;
        foreach(var item in sequence)
        {
            if (first == null)
                first = item;
            else if (comparer != null && !comparer.Equals(first, item))
                return other;
            else if (!first.Equals(item))
                return other;
        }
        return (Nullable)first ?? other;
    }

    public static T Unanimous(this IEnumerable sequence, T other, IEqualityComparer comparer = null)  where T : class, IComparable
    {
        object first = null;
        foreach(var item in sequence)
        {
            if (first == null)
                first = item;
            else if (comparer != null && !comparer.Equals(first, item))
                return other;
            else if (!first.Equals(item))
                return other;
        }
        return (T)first ?? other;
    }
}