The Wiert Corner – irregular stream of stuff

When you have a Dictionary<TKey, TValue>, then LINQ results will get you a enumerables of KeyValuePair<TKey, TValue>.

Since KeyValuePair is a struct, selecting FirstOrDefault will not get you a null, but a default(KeyValuePair<TKey, TValue>) which is a lot harder to handle than null.

Sometimes, being able to get a null out of FirstOrDefault is very useful, so a bit thank you to Marc Gravell for answering this very neat trick:

If you just care about existence, you could use ContainsValue(0) or Any(p => p.Value == 0) instead? Searching by value is unusual for a Dictionary<,>; if you were searching by key, you could use TryGetValue.

One other approach:

       var record = data.Where(p => p.Value == 1)
            .Select(p => new { Key = p.Key, Value = p.Value })
            .FirstOrDefault();

This returns a class – so will be null if not found.

The trick is this portion:

p => new { Key = p.Key, Value = p.Value }

It introduces an anonymous type with two fields: Key and Value. (Note you can introduce any anonymous type here). Since these are classes, FirstOrDefault will return null if nothing was found.

–jeroen

via:

• c# – Check if KeyValuePair exists with LINQ’s FirstOrDefault – Stack Overflow.
• c# – How can I make sure that FirstOrDefault has returned a value – Stack Overflow.