public static List <T> Sample <T>(this IList <T> self, bool replacement = false, int sampleSize = -1, IRandom random = null)
{
if (sampleSize == -1)
{
sampleSize = self.Count;
}
if (replacement)
{
random ??= RandomInstance.Get();
var result = new List <T>(sampleSize);
for (var i = 0; i < sampleSize; ++i)
{
var j = random.Next(self.Count);
result.Add(self[j]);
}
return(result);
}
else
{
if (sampleSize > self.Count)
{
throw new ArgumentOutOfRangeException("sampleSize", "Sample size must not be larger than the size of the population without replacement.");
}
var result = Shuffle(self, random);
if (sampleSize == self.Count)
{
return(result);
}
return(result.Take(sampleSize).ToList());
}
}
public static void ShuffleFill <T>(this IList <T> self, IRandom random = null)
{
random ??= RandomInstance.Get();
for (var i = 0; i < self.Count; ++i)
{
var j = random.Next(i + 1);
var temp = self[i];
self[i] = self[j];
self[j] = temp;
}
}
public static List <T> Shuffle <T>(this IList <T> self, IRandom random = null)
{
// ref: https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle
var result = new List <T>(self.Count);
random ??= RandomInstance.Get();
for (var i = 0; i < self.Count; ++i)
{
var j = random.Next(i + 1);
if (j == i)
{
result.Add(self[i]);
}
else
{
result.Add(result[j]);
result[j] = self[i];
}
}
return(result);
}
