/// <summary>
/// Randomizes the order of the list in-place with the Fisher-Yates shuffle.
/// </summary>
/// <param name="rng">The random number generator to use.</param>
/// <returns>The shuffled list.</returns>
public static IList <T> Shuffle <T>(this IList <T> list, IAltRandom rng)
{
for (int i = 0; i < list.Count - 2; i++)
{
int j = rng.RandInt(i, list.Count - 1);
T temp = list[i];
list[i] = list[j];
list[j] = temp;
}
return(list);
}
/// <summary>
/// Samples from the list <em>without replacement</em>.
/// </summary>
/// <param name="number">The number of samples to take.</param>
/// <param name="rng">The random number generator to use.</param>
/// <returns>A list of elements from this list with unique indices.</returns>
public static IList <T> Sample <T>(this IList <T> list, int number, IAltRandom rng)
{
if (list == null)
{
throw new ArgumentNullException("list");
}
if (list.Count < number)
{
throw new ArgumentException(
String.Format("List has only {0} items; cannot take {1} samples", list.Count, number)
);
}
IList <T> pool = new List <T>(list);
IList <T> result = new List <T>(new T[number]);
for (int i = 0; i < number; i++)
{
int j = rng.RandIndex(pool.Count - i);
result[i] = pool[j];
pool[j] = pool[pool.Count - i - 1];
}
return(result);
}
/// <summary>
/// Constructs a wrapper around an <see cref="IAltRandom"/> object.
/// The resulting objects behaves as an ordinary <see cref="System.Random"/> instance as much as possible,
/// except it uses better algorithms.
/// </summary>
/// <param name="wrapped">The <see cref="IAltRandom"/> object to be encapsulated.</param>
public SystemRandomWrapper(IAltRandom wrapped)
{
rng = wrapped;
}
