Question

I have a list of objects

class Answer
{
   bool correct;
}

List<Answer> Answers = new List<Answer>();

Is there a way in linq for me to select an object depending on its attribute?

So far I have

Answer answer = Answers.Single(a => a == a.Correct);

But it does not work

Answer 1

First, Single throws an exception if there is more than one element satisfying the criteria. Second, your criteria should only check if the Correct property is true. Right now, you are checking if a is equal to a.Correct (which will not even compile).

You can also consider using First (which will throw if there are no such elements), or FirstOrDefault (which will return null for a reference type if there isn’t such element), or Where followed by ToList (which will return all elements which satisfy the criteria):

// this will either find a single correct answer,
// or throw an exception if there are no correct answers
// or if there is more than one correct answer
var correct = answers.Single(a => a.Correct);

// this will either find a single correct answer,
// or return null if there are no correct answers,
// or throw an exception if there is more than one correct answer
var correct = answers.SingleOrDefault(a => a.Correct);

// this will return the first correct answer,
// or throw an exception if there are no correct answers
var correct = answers.First(a => a.Correct); 

// this will return the first correct answer, 
// or null if there are no correct answers
var correct = answers.FirstOrDefault(a => a.Correct); 

// this will return a list containing all answers which are correct,
// or an empty list if there are no correct answers
var allCorrect = answers.Where(a => a.Correct).ToList();