Convert List<T> to T item if there is only one element?

Question

I have a List<> with N items. I want to get the first element if and only if N = 1. Can this be done using lambda or some other nice construct?

This works, but looks horrible:

var blah = new List<Object>() { new Object() };
var item = (blah.Count == 1 ? blah[0] : null);

Answer 1

There are several LINQ extension methods.

1. SingleOrDefault If there is one element it will be returned, if there are none default<T> will be returned, if there are multiple an exception is thrown
2. FirstOrDefault If there is one element it will be returned, if there are none default<T> will be returned
3. ElementAtOrDefault returns the element at the given position or default<T> if the sequence has not so many elements

So for example (my preferred for your requirement):

var item = blah.ElementAtOrDefault(0);

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The best method for your requirement depends on how strict this rule is:

I want to get the first element if and only if N = 1.

If it's exceptional that there is more than one element in the sequence, use SingleOrDefault and you'll be informed (error-log) if it gets out of hand.

If it's important that you get the first element and you'll never want another element, use better FirstOrDefault because it has a meaningful name.

If the index of the element in the sequence is important and you (currently) need the first element, but that might change in future, use ElementAtOrDefault.