/// <summary>
/// Get a random subset of the specified size from the provided List.
/// </summary>
public static IList <T> RandomSubset <T>(this IList <T> list, int n, System.Random rng = null)
{
if (list.Count < n)
{
throw new ArgumentOutOfRangeException($"Can't select a random subset of {n} items from a list of {list.Count} items.");
}
if (rng == null)
{
rng = _rng;
}
IList <int> indices = rng.Distinct(n, 0, list.Count);
List <T> output = new List <T>(n);
foreach (int index in indices)
{
output.Add(list[index]);
}
return(output);
}
/// <summary>
/// Generate N random positive (optionally including 0) integers that sum to the specified
/// total.
/// </summary>
public static IList <int> SumTo(
this System.Random rng,
int n,
int sum,
bool allowZero = false
)
{
if (n <= 0 || sum <= 0)
{
throw new ArgumentException($"Can't generate {n} numbers that sum to {sum}.");
}
if (!allowZero && n > sum)
{
throw new ArgumentException($"Can't generate {n} non-zero numbers that sum to {sum}.");
}
// Generate a list of N-1 random numbers between 0 and sum, which will act as
// partition points between the output random numbers.
IList <int> divisions = allowZero
? rng.Many(n - 1, 0, sum, true)
: rng.Distinct(n - 1, 1, sum, true);
// Add each partition width to the list of output numbers.
List <int> output = new List <int>();
int lastDivision = 0;
for (int i = 0; i < divisions.Count; ++i)
{
output.Add(divisions[i] - lastDivision);
lastDivision = divisions[i];
}
output.Add(sum - lastDivision);
return(output);
}