using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        List<int> days = new List<int>();

        days.Add(1);

        days.Add(2);

        days.Add(3);

        days.Add(4);

        days.Add(5);

        days.Add(6);

        days.Add(7);

        List<LinqTest> testList = new List<LinqTest>();

        testList.Add(new LinqTest() { id = 1234, date = 3, employeeCount = 30});

        testList.Add(new LinqTest() { id = 1235, date = 2, employeeCount = 100});

        testList.Add(new LinqTest() { id = 1236, date = 3, employeeCount = 60});

        testList.Add(new LinqTest() { id = 1237, date = 4, employeeCount = 45});

        testList.Add(new LinqTest() { id = 1238, date = 5, employeeCount = 13});

        testList.Add(new LinqTest() { id = 1234, date = 6, employeeCount = 2});

        testList.Add(new LinqTest() { id = 1234, date = 7, employeeCount = 200});

        testList.Add(new LinqTest() { id = 1234, date = 2, employeeCount = 36});

        testList.Add(new LinqTest() { id = 1236, date = 6, employeeCount = 2});

        testList.Add(new LinqTest() { id = 1234, date = 6, employeeCount = 100});

        //testList.Add(new LinqTest() { id = 1234, date = DateTime.Parse("05/16/2016"), employeeCount = 1});

        //testList.Add(new LinqTest() { id = 1234, date = DateTime.Parse("05/17/2016"), employeeCount = 76});

        var itemsWithDefaults = (from d in days

            join l in testList on d equals l.date into dl

            from dayList in dl.DefaultIfEmpty()

            select new LinqTest() {

            id = dayList == null ? 0 : dayList.id,

            date = d,

            employeeCount = dayList == null ? 0 : dayList.employeeCount

        }).ToList();

        var map = itemsWithDefaults

          .GroupBy(x => x.date)

          .ToDictionary(x => x.Key, x => x.ToList());

        //nsole.WriteLine(map.FirstOrDefault());

        foreach(var key in map)

        {

            Console.WriteLine(key.Key);

            foreach(var item in key.Value)

            {

                Console.WriteLine(item.id);

            }

            Console.WriteLine(key.Value.Sum(v => v.employeeCount));

        }

        var nextDay = 0;

        nextDay = (int)map.OrderBy(m => m.Value.Sum(v => v.employeeCount)).ThenBy(m => (int)m.Key).FirstOrDefault().Key;

        Console.WriteLine((DayOfWeek)nextDay);

        //nsole.WriteLine(map.Keys.Count());

        //var ret = map.Keys.Count();

        //Console.WriteLine("Hello World " + ret);

    }

}

​

public class LinqTest

{

public int id { get; set; }

public int date { get; set; }

public int employeeCount { get; set; }

}