You can use a Fisher-Yates-Durstenfeld shuffle. There’s no need to explicitly pass a size argument to the method itself, you can simply tack on a call to Take
if you don’t need the entire sequence:
var shuffled = originalSequence.Shuffle().Take(5);
// ...
public static class EnumerableExtensions
{
public static IEnumerable<T> Shuffle<T>(this IEnumerable<T> source)
{
return source.Shuffle(new Random());
}
public static IEnumerable<T> Shuffle<T>(this IEnumerable<T> source, Random rng)
{
if (source == null) throw new ArgumentNullException(nameof(source));
if (rng == null) throw new ArgumentNullException(nameof(rng));
return source.ShuffleIterator(rng);
}
private static IEnumerable<T> ShuffleIterator<T>(
this IEnumerable<T> source, Random rng)
{
var 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];
}
}
}