StatisticsTask.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;

namespace linq_slideviews
{
	public class StatisticsTask
	{
		public static double GetMedianTimePerSlide(List<VisitRecord> visits, SlideType slideType)
		{
			List<double> minutes = new List<double>();
			var visitsByUsers = visits.GroupBy(visit => visit.UserId);
			foreach (var visitsByUser in visitsByUsers)
				CalculateMinutesForAllSlidesForOneUser(visitsByUser.OrderBy(visit => visit.DateTime).Bigrams(), minutes, slideType);
			if (minutes.Count == 0)
				return 0;
			return ExtensionsTask.Median(minutes);
		}

		static void CalculateMinutesForAllSlidesForOneUser
			(IEnumerable<Tuple<VisitRecord, VisitRecord>> bigramsOfVisitsByOneUser, List<double> minutes, SlideType slideType)
		{
			double minutesToAdd = 0;
			foreach (var bigramOfVisits in bigramsOfVisitsByOneUser)
			{
				if (bigramOfVisits.Item1.SlideType == slideType)
				{
					minutesToAdd += (bigramOfVisits.Item2.DateTime - bigramOfVisits.Item1.DateTime).TotalMinutes;
					if (bigramOfVisits.Item1.SlideId != bigramOfVisits.Item2.SlideId)
					{
						if (minutesToAdd >= 1 && minutesToAdd <= 120)
							minutes.Add(minutesToAdd);
						minutesToAdd = 0;
					}
				}
			}
			if (minutesToAdd >= 1 && minutesToAdd <= 120)
				minutes.Add(minutesToAdd);
		}
	}
}