/// <summary>
/// Returns a random sample of size k from a population of size n.
/// </summary>
public static int[] Random(int n, int k)
{
var r = new Random();
// If the sample is a sizeable fraction of the population, just
// randomize the whole population (which involves a full sort
// of n random values), and take the first k.
if (4 * k > n)
{
int[] idx = Tools.Random(n);
return(idx.Submatrix(k));
}
else
{
int[] x = new int[n];
int sumx = 0;
while (sumx < k)
{
x[r.Next(0, n)] = 1;
sumx = Accord.Math.Matrix.Sum(x);
}
int[] y = x.Find(z => z > 0);
return(y.Submatrix(Random(k)));
}
}
