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

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;