score:3

Assuming Gregorian calendar, "first day" week rule and that the first day of the week is Monday.

First day week rule:

Indicates that the first week of the year starts on the first day of the year and ends before the following designated first day of the week

``````int firstDayOfWeek = (int)DayOfWeek.Monday;
var q =
from u in TblUsers
let date = u.CreateDate.Value
let num = date.DayOfYear - 1
let num2 = ((int)date.DayOfWeek) - (num % 7)
let num3 = ((num2 - firstDayOfWeek) + 14) % 7
let week = (((num + num3) / 7) + 1)
group u by week into g
select new
{
Week = g.Key,
Count = g.Count ()
};
``````

score:0

Hope this helps:

``````    var d1 = new DateTime(1990, 1, 1);
var d2 = new DateTime(1990, 1, 2);
var d3 = new DateTime(1990, 1, 11);
var d4 = new DateTime(1990, 1, 12);

var records = new[] {
new { date = d1, freq = 1 },
new { date = d2, freq = 2 },
new { date = d3, freq = 3 },
new { date = d4, freq = 4 }
};

//ticks * WeekDays * DayHours * HourMins * MinSecs
var weekTicks = (Int64)10000000 * 7 * 24 * 60 * 60;
var res = records.GroupBy(x => x.date.Ticks / weekTicks)
.Select(x => new { week=x.Key ,sum=x.Sum(y=>y.freq)});
``````

And this is the result:

[0] = { week = 99085, sum = 3 }

[1] = { week = 99086, sum = 7 }