/// <summary>
/// Updates the sample set adding the specified value using <see href="http://www.cs.umd.edu/~samir/498/vitter.pdf">Vitter's Algorithm R</see>.
/// </summary>
/// Algorithm R pseudo code
/// <example>
/// <code>
/// <![CDATA[
/// -- S has items to sample, R will contain the result
/// ReservoirSample(S[1..n], R[1..k])
/// -- fill the reservoir array
/// for i = 1 to k
/// R[i] := S[i]
/// -- replace elements with gradually decreasing probability
/// for i = k+1 to n
/// j := random(1, i) -- important: inclusive range
/// if j <= k
/// R[j] := S[i]
/// ]]>
/// </code>
/// </example>
/// <param name="value">The value to add to the sample set.</param>
/// <param name="userValue">The user value to track, which records the last, min and max user values within the sample.</param>
public void Update(long value, string userValue = null)
{
var c = _count.Increment();
if (c <= _values.Length)
{
_values[(int)c - 1] = new UserValueWrapper(value, userValue);
}
else
{
var r = ThreadLocalRandom.NextLong(c);
if (r < _values.Length)
{
_values[(int)r] = new UserValueWrapper(value, userValue);
}
}
}
public bool Equals(UserValueWrapper other)
{
return(string.Equals(UserValue, other.UserValue) && Value == other.Value);
}
