ASP.NET MVC 按周过滤日期时间

Question

I've got a Web API and a Get method, returning a query:

var query = from results in context.Table
            where results.Date>= startDate && results.Date <= endDate
            select new 
{ 
Week = { this is where I need a method to group by weeks },
Average = results.Where(x => x.Number).Average()
}

return query.ToList();

I want to calculate the average for each 7 days (that being the first week).

Example:

Average 1 ... day 7 (Week 1)
Average 2 ... day 14 (Week 2)

How can I do that? Being given an interval of datetimes, to filter it by weeks (not week of year)

Answer 1

Why not write a stored procedure, I think there may be some limitations on your flexibility using Linq because of the idea that normally the GroupBy groups by value (the value of the referenced "thing") so you can group by State, or Age, but I guess you can Group week... (new thought)

Add a property called EndOfWeek and for example, the end of this week is (Sunday let's say) then EndOfWeek = 9.2.16 whereas last week was 8.28.16... etc. then you can easily group but you still have to arrange the data.

I know I didn't answer the question but I hope that I sparked some brain activity in an area that allows you to solve the problem.

--------- UPDATED ----------------

simple solution, loop through your records, foreach record determine the EndOfWeek for that record. After this you will now have a groupable value. Easily group by EndOfWeek. Simple!!!!!!!!!!!! Now, @MikeMcCaughan please tell me how this doesn't work? Is it illogical to extend an object? What are you talking about?

------------ HERE IS THE CODE ----------------

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace SandboxConsole
{
class Program
{
    static void Main(string[] args)
    {
        var t = new Transactions();
        List<Transactions> transactions = t.GetTransactions();

        // Now let's add a Weeks end date so we can determine the average per week
        foreach(var transaction in transactions)
        {
            var transactionDayOfWeek = transaction.TransactionDate;
            int daysUntilEndOfWeek_Sat = ((int)DayOfWeek.Saturday - (int)transactionDayOfWeek.DayOfWeek + 7) % 7;
            transaction.Newly_Added_Property_To_Group_By_Week_To_Get_Averages = transactionDayOfWeek.AddDays(daysUntilEndOfWeek_Sat).ToShortDateString();
            //Console.WriteLine("{0} {")
        }

        foreach(var weekEnd in transactions.GroupBy(tt => tt.Newly_Added_Property_To_Group_By_Week_To_Get_Averages))
        {
            decimal weekTotal = 0;
            foreach(var trans in weekEnd)
            {
                weekTotal += trans.Amount;
            }

            var weekAverage = weekTotal / 7;
            Console.WriteLine("Week End: {0} - Avg {1}", weekEnd.Key.ToString(), weekAverage.ToString("C"));
        }
        Console.ReadKey();
    }
}

class Transactions
{
    public int Id { get; set; }
    public string SomeOtherProp { get; set; }
    public DateTime TransactionDate { get; set; }
    public decimal Amount { get; set; }
    public string Newly_Added_Property_To_Group_By_Week_To_Get_Averages { get; set; }

    public List<Transactions> GetTransactions()
    {
        var results = new List<Transactions>();

        for(var i = 0; i<100; i++)
        {
            results.Add(new Transactions
            {
                Id = i,
                SomeOtherProp = "Customer " + i.ToString(),
                TransactionDate = GetRandomDate(i),
                Amount = GetRandomAmount()
            });
        }

        return results;
    }

    public DateTime GetRandomDate(int i)
    {
        Random gen = new Random();
        DateTime startTime = new DateTime(2016, 1, 1);
        int range = (DateTime.Today - startTime).Days + i;
        return startTime.AddDays(gen.Next(range));
    }
    public int GetRandomAmount()
    {
        Random rnd = new Random();
        int amount = rnd.Next(1000, 10000);
        return amount;
    }
}

}

------------ OUTPUT --------------- Sample Output

Answer 2

Try this (not tested with tables)

var avgResult = context.QuestionaireResults
               .Where(r => (r.DepartureDate >= startDate && r.DepartureDate <= endDate)).ToList()
               .GroupBy( g => (Decimal.Round(g.DepartureDate.Day / 7)+1))
               .Select( g => new
                {
                   Week = g.Key,
                   Avg = g.Average(n => n.Number)
                }); 

Answer 3

You will need to group by the number of days, since a reference date, divided by 7, so

.GroupBy(x => Math.Floor(((x.DepartureDate - new DateTime(1980,1,1)).TotalDays + 2) / 7))

Subtracting "Jan 1, 1980" from your departure date, gives you a TimeSpan object with the difference between the two dates. The TotalDays property of that timespan gives you timespan in days. Adding 2 corrects for the fact that "Jan 1, 1980" was a Tuesday. Dividing by 7 gives you the number of weeks since then. Math.Floor rounds it down, so that you get a consistent integer for the week, given any day of the week or portion of days within the week.

You could simplify a little by picking a reference date that is a Sunday (assuming that is your "first day of the week"), so you dont have to add 2 to correct. Like so:

.GroupBy(x => Math.Floor(((x.DepartureDate - new DateTime(1979,12,30)).TotalDays) / 7))

If you are sure that your data all falls within a single calendar year, you could maybe use the Calendar.GetWeekOfYear method to figure out the week, but I am not sure it would be any simpler.