Returning data related to a day without duplication using linq and C#

Question

The query below returns the sample data below. There are multiple days. I want to be able to display the day with the associated data under each day. My expected result can also be found below. Somehow I think I need to use a nested foreach statement but have been unable to figure this out. I am new to Linq. Please assist if you have any idea.

            var pracResult = from t in queryResultFilter
                                             orderby t.Day
                                             select t;
                            Int32 okeke = 0;

                            foreach (MyPlanDto chk in pracResult)
                            {
                                okeke = chk.Day;
                            }

            Sample data
            *************

            Day = Monday
            CustomerNumber = 1001
            Product = Dress

            Day = Tuesday
            customerNumber = 1002
            Product = Boxers

            Day = Wednesday
            CustomerNumber = 1003
            Product = Pencil

            Day = Monday
            CustomerNumber = 1006
            Product = Pen

            Day = Monday
            CustomerNumber = 1007
            Product = Book

            Day = Tuesday
            CustomerNumber = 1008
            Product = Erazer

            Result:
            ********

            Monday
            ********
            CustomerNumber = 1001
            Product = Dress

            CustomerNumber = 1006
            Product = Pen

            CustomerNumber = 1007
            Product = Book

            Tuesday
            ********
            customerNumber = 1002
            Product = Boxers

            CustomerNumber = 1008
            Product = Erazer

            Wednesday
            ***********
            CustomerNumber = 1003
            Product = Pencil

Here is an example I tried but not working.

        using System;
        using System.Collections.Generic;
        using System.Linq;

        namespace MasterData
        {
            class Program
            {
                static void Main(string[] args)
                {

                    var queryResultFilter = ObjMyPlan();



                    var pracResult = (from t in queryResultFilter
                        orderby t.Day
                        select t).ToLookup(p => p.Day).Select(col1 => col1.First());

                    var pracResult2 = (from t in queryResultFilter
                                      orderby t.Day
                                      select t);


                    foreach (MyPlanDto chk in pracResult)
                    {

                        Console.WriteLine(chk.Day);

                        foreach (MyPlanDto obj1 in pracResult2)
                        {
                            var yoyou = (from t in pracResult2
                                           select t).Where(p=>p.Day.Equals(chk.Day));
                            Console.WriteLine("Customer Number:" + obj1.CustomerNumber + "Product:" + obj1.Product);
                        }

                    }
                    Console.ReadKey();

                }


                static List<MyPlanDto> ObjMyPlan()
                {
                    List<MyPlanDto> objResult = new List<MyPlanDto>();
                    objResult.Add(new MyPlanDto(){Day = "Monday", CustomerNumber = "1001", Product = "Dress"});
                    objResult.Add(new MyPlanDto(){Day = "Tuesday", CustomerNumber = "1002", Product = "Boxers"});
                    objResult.Add(new MyPlanDto(){Day = "Wednesday", CustomerNumber = "1003", Product = "Pencil"});
                    objResult.Add(new MyPlanDto(){Day = "Monday", CustomerNumber = "1006", Product = "Pen"});
                    objResult.Add(new MyPlanDto(){Day = "Monday", CustomerNumber = "1007", Product = "Book"});
                    objResult.Add(new MyPlanDto(){Day = "Tuesday", CustomerNumber = "1008", Product = "Erazer"});

                    return objResult;
                }

            }
        }

Answer 1

You're close with the ToLookup approach. You should be able to use a query like this:

var query = queryResultFilter.OrderBy(t => t.Day)
                             .ToLookup(t => t.Day);

foreach (var group in query) {
    Console.WriteLine(group.Key);
    foreach (var item in group) {
        Console.WriteLine("CustomerNumber: {0}", item.CustomerNumber);
        Console.WriteLine("Product: {0}", item.Product);
    }
    Console.WriteLine();
}

Alternately, typically the first option that comes to mind is to use grouping, which offers deferred execution compared to ToLookup. Either of these queries would work (and you can use the same foreach loop above):

var query = queryResultFilter.OrderBy(t => t.Day)
                             .GroupBy(t => t.Day);

// query syntax
var query = from t in queryResultFilter
            orderby t.Day
            group t by t.Day into grouped
            select grouped;

If you're curious about the difference between ToLookup and GroupBy, check out this post.

Note that ordering by t.Day is alphabetical, so does it really serve the purpose you intend? If you have "Friday" in your data it will show up before "Wednesday" when ordered. If you have dates, that would work better if you really need to order the results.