Linq: How to get a Random Object using Linq

Question

I am trying to get a random object within linq. Here is how I did.

            //get all the answers
            var Answers = q.Skip(1).Take(int.MaxValue);

            //get the random number by the number of answers
            int intRandomAnswer = r.Next(1, Answers.Count());
            int count = 0;

            //locate the answer
            foreach(var Answer in Answers)
            {
                if (count == intRandomAnswer)
                {
                    SelectedPost = Answer;
                    break;
                }
                count++;
            }

Is this the best way to do this?

Answer 1

What about:

SelectedPost = q.ElementAt(r.Next(1, Answers.Count()));

Answer 2

Pulling all of the answers and looping them isn't the most efficient way as you're moving lots of data from the database. If you're using an integer primary key that's automatically incrementing, you should get the Max of your primary key and then find the random integer within that range. Then directly get the single answer based on the primary key derived from the random function.

Answer 3

Another wacky approach (not the most efficient for larger data sets):

SelectedPost = q.OrderBy(qu => Guid.NewGuid()).First();

Answer 4

Use a Fisher-Yates-Durstenfeld shuffle. Here's a general purpose extension method that does just that:

// use First for a single random answer or Take(n) for multiple answers
var SelectedPost = Answers.Shuffle().First();

// ...

public static class EnumerableExtensions
{
    public static IEnumerable<T> Shuffle<T>(this IEnumerable<T> source)
    {
        // error checking etc removed for brevity

        Random rng = new Random();
        T[] sourceArray = source.ToArray();

        for (int n = 0; n < sourceArray.Length; n++)
        {
            int k = rng.Next(n, sourceArray.Length);
            yield return sourceArray[k];

            sourceArray[k] = sourceArray[n];
        }
    }
}