public void Sample()
{
Contracts.Check(!_locked, "Cannot continue to sample after Lock() has been called");
_numSampled++;
// If the number of samples seen so far is less than the total reservoir size, cache the new sample.
if (_numSampled <= _cache.Length)
{
_getter(ref _cache[_numSampled - 1]);
// If the cache is full, sample from it with replacement into the reservoir.
if (_numSampled == _cache.Length)
{
for (int i = 0; i < _cache.Length; i++)
{
_reservoir[i] = _rnd.Next(_cache.Length);
_counts[_reservoir[i]]++;
}
}
}
else
{
// Choose how many times to insert the current instance into the reservoir.
int k = Stats.SampleFromBinomial(_rnd, _cache.Length, 1.0 / _numSampled);
if (k > 0)
{
int ind = _rnd.Next(_reservoir.Length);
// If the item referenced at this index appears more than once in the reservoir, we cannot overwrite it,
// we need to find an available place in the cache.
if (_counts[_reservoir[ind]] > 1)
{
Contracts.Assert(_counts.Contains(0));
var tmp = _counts.Select((count, i) => new KeyValuePair <int, int>(count, i)).First(kvp => kvp.Key == 0);
_counts[_reservoir[ind]]--;
_reservoir[ind] = tmp.Value;
_counts[tmp.Value] = 1;
}
else if (_counts[_reservoir[ind]] == 0)
{
_counts[_reservoir[ind]]++;
}
_getter(ref _cache[_reservoir[ind]]);
for (int j = 1; j < k;)
{
var next = _rnd.Next(_reservoir.Length);
if (_reservoir[next] == _reservoir[ind])
{
continue;
}
_counts[_reservoir[next]]--;
_reservoir[next] = _reservoir[ind];
_counts[_reservoir[next]]++;
j++;
}
}
}
}
/// <summary>
/// Defines a sample stream for a biniomian distribution
/// </summary>
/// <param name="random">The random source</param>
/// <param name="n">The number of trials</param>
/// <param name="p">The probability of success of a given trial</param>
public static IEnumerable <int> SampleBinomial(this IPolyrand random, int n, double p)
{
var sysrand = SysRand.Derive(random);
while (true)
{
yield return(MlStats.SampleFromBinomial(sysrand, n, p));
}
}
/// <summary>
/// Defines a sample stream for a biniomian distribution
/// </summary>
/// <param name="random">The random source</param>
/// <param name="n">The number of trials</param>
/// <param name="p">The probability of success of a given trial</param>
public static IEnumerable <T> SampleBinomial <T>(this IPolyrand random, T n, double p)
where T : struct
{
var sysrand = SysRand.Derive(random);
while (true)
{
yield return(convert <T>(MlStats.SampleFromBinomial(sysrand, convert <T, int>(n), p)));
}
}