Getting random numbers from a list of integers

Question

If I have a list of integers:

List myValues = new List(new int[] { 1, 2, 3, 4, 5, 6 } );

How would I get 3 random integer

Answer 1

One simple way:

Random r = new Random();
IEnumerable threeRandom = myValues.OrderBy(x => r.Next()).Take(3);

The better way: Fisher–Yates shuffle:

public static class EnumerableExtensions
{
    public static IEnumerable Shuffle(this IEnumerable source)
    {
        return source.Shuffle(new Random());
    }

    public static IEnumerable Shuffle(this IEnumerable source, Random rng)
    {
        if (source == null) throw new ArgumentNullException("source");
        if (rng == null) throw new ArgumentNullException("rng");

        return source.ShuffleIterator(rng);
    }

    private static IEnumerable ShuffleIterator(
        this IEnumerable source, Random rng)
    {
        List buffer = source.ToList();
        for (int i = 0; i < buffer.Count; i++)
        {
            int j = rng.Next(i, buffer.Count);
            yield return buffer[j];

            buffer[j] = buffer[i];
        }
    }
}

how you use it:

IEnumerable threeRandom = myValues.Shuffle().Take(3);