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

An alternative to using LINQ:

var set = new HashSet<int>(values);
return (1 == set.Count) ? values.First() : otherValue;

I have found using HashSet<T> is quicker for lists of up to ~ 6,000 integers compared with:

var value1 = items.First();
return values.All(v => v == value1) ? value1: otherValue;

Answer 2

return collection.All(i => i == collection.First())) 
    ? collection.First() : otherValue;.

Or if you're worried about executing First() for each element (which could be a valid performance concern):

var first = collection.First();
return collection.All(i => i == first) ? first : otherValue;

Answer 3

Good quick test for all equal:

collection.Distinct().Count() == 1