/*

LINQ includes five sorting operators: OrderBy, OrderByDescending, ThenBy, ThenByDescending and Reverse

LINQ query syntax does not support OrderByDescending, ThenBy, ThenByDescending and Reverse. It only supports 'Order By' clause with 'ascending' and 'descending' sorting direction.

LINQ query syntax supports multiple sorting fields seperated by comma whereas you have to use ThenBy & ThenByDescending methods for secondary sorting.

​

OrderBy and ThenBy sorts collections in ascending order by default.

ThenBy or ThenByDescending is used for second level sorting in method syntax.

ThenByDescending method sorts the collection in decending order on another field.

ThenBy or ThenByDescending is NOT applicable in Query syntax.

Apply secondary sorting in query syntax by separating fields using comma.

​

*/

​

using System;

using System.Linq;

using System.Collections.Generic;

​

class Student

{

    public int StudentID { get; set; }

    public String StudentName { get; set; }

    public int Age { get; set; }

}

​

public class Program

{

    public static void Main()

    {

        IList<Student> studentList = new List<Student>() 

        { 

            new Student() { StudentID = 1, StudentName = "John", Age = 18 } ,

            new Student() { StudentID = 2, StudentName = "Steve",  Age = 15 } ,

            new Student() { StudentID = 3, StudentName = "Bill",  Age = 25 } ,

            new Student() { StudentID = 4, StudentName = "Ram" , Age = 25 } ,

            new Student() { StudentID = 5, StudentName = "Ron" , Age = 15 } 

        };

​

        //OrderBy, OrderByDescending, ThenBy, ThenByDescending  - Method Syntax

        //Use ThenBy for multiple field sorting.

        Console.WriteLine("OrderBy, ThenBy - Method Syntax\n -------------------------------" );

        var result = studentList.OrderByDescending(s => s.StudentName).ThenByDescending(s => s.StudentID);

        foreach (Student std in result)

        {

            Console.WriteLine(std.StudentID + " - " + std.StudentName + " - " + std.Age);

        }

        Console.WriteLine("\n orderby - Query Syntax \n------------------------ ");

        //Order By(multiple fields) - query syntax      

        var objList = from s in studentList orderby s.StudentName descending, s.StudentID descending select new {Id = s.StudentID, s.StudentName, s.Age};

        foreach (Object std in objList)

        {           

            Console.WriteLine(std);

        }

        Console.WriteLine("\n GroupBy - query Syntax \n ------------------------ ");

        var objBY = from s in studentList group s by new {s.Age} into g select g ;

        foreach(var groupby in objBY)

        {

            Console.WriteLine(groupby.Key.Age);

            foreach(Student stud in groupby)

            {

                Console.WriteLine(stud.StudentID + " - " + stud.StudentName + " - " + stud.Age) ;

            }

        }

        Console.WriteLine("\n GroupBy & OrderBy - Method Syntax \n --------------------------------");

        var methGB = studentList

                        .GroupBy(item => new {item.Age})

                        .Select(item1 => new {ID = item1.Last().StudentID, StudentName = item1.Last().StudentName, Age = item1.Last().Age})

                        .OrderBy(item2 => item2.ID).ThenBy(item3 => item3.StudentName);

        foreach(var groupby in methGB)

        {

            Console.WriteLine(groupby);

            /*foreach(Student stud in groupby)

            {

                Console.WriteLine(stud.StudentID + " - " + stud.StudentName + " - " + stud.Age) ;

            }*/

        }   

        Console.WriteLine("\n ToLookUp - Method Syntax \n -------------------------");

        var lookup = studentList.ToLookup(item => item.Age);

        foreach(var groupby in lookup)

        {

            Console.WriteLine(groupby.Key);

            foreach(Student stud in groupby)

            {

                Console.WriteLine(stud.StudentID + " - " + stud.StudentName + " - " + stud.Age) ;

            }

        }   

    }

}