ExponentiallyDecayingSampleTests.cs

using NUnit.Framework;
using metrics.Stats;

namespace metrics.Tests.Stats
{
    [TestFixture]
    public class ExponentiallyDecayingSampleTests
    {
        [Test]
        public void HoldsRequestedNumberOfSamples()
        {
            var reservoirSize = 1000;
            var sample = new ExponentiallyDecayingSample(reservoirSize, 0);
            for (var i = 0; i < reservoirSize; i++)
            {
                sample.Update(i);
            }
            Assert.AreEqual(reservoirSize, sample.Count);
            Assert.AreEqual(reservoirSize, sample.Values.Count);
        }
    }
}

gistfile1.cs

public class WebBase : NancyModule
{
    private ExponentiallyDecayingSample _sample;

    public WebBase()
    {
        Setup();

        Get["/sampling"] = param =>
        {
            _sample.Clear();

            for (int i = 0; i < 100; i++)
            {
                _sample.Update(i);
            }

            var values = new List<long>(_sample.Values);
            values.Sort();

            return string.Join(",", values);
        };
    }

    private void Setup()
    {
        _sample = new ExponentiallyDecayingSample(1024, 0.15);
    }
}