GroupBy & Join Linq C#

Group By Linq

• powerful feature of linq Similar to Group by as SQL
• It can be done using both linq as well as lambda expression.

Code

using System;  
 using System.Collections.Generic;  
 using System.Linq;  
 namespace XML  
 {  
   class Program  
   {  
     public class student  
     {  
       public int id { get; set; }  
       public string name { get; set; }  
       public int classId { get; set; }  
       public List<student> getStudents()  
       {  
         List<student> obj = new List<student>();  
         obj.Add(new student { id = 101, name = "abc1", classId = 1 });  
         obj.Add(new student { id = 102, name = "abc2", classId = 1 });  
         obj.Add(new student { id = 103, name = "abc3", classId = 2 });  
         obj.Add(new student { id = 104, name = "abc4", classId = 2 });  
         obj.Add(new student { id = 105, name = "abc5", classId = 2 });  
         obj.Add(new student { id = 106, name = "abc6", classId = 3 });  
         obj.Add(new student { id = 107, name = "abc7", classId = 3 });  
         obj.Add(new student { id = 108, name = "abc8", classId = 3 });  
         obj.Add(new student { id = 109, name = "abc9", classId = 3 });  
         return obj;  
       }  
     }  
     static void Main(string[] args)  
     {  
       student s = new student();  
       var students = s.getStudents().ToList();  
       var final = students.GroupBy(x => x.classId).ToDictionary(y => y.Key, y => y.ToList());  
       foreach (var x in final)  
       {  
         Console.WriteLine("----" + x.Key + "-----");  
         foreach (var item in x.Value)  
         {  
           Console.WriteLine(item.id);  
           Console.WriteLine(item.name);  
           Console.WriteLine();  
         }  
         Console.WriteLine("===================================");  
       }  
       Console.WriteLine("--------Slight Modification----------");  
       var final1 = students.GroupBy(x => x.classId).Select(g => new { Key=g.Key, List=g.ToList() });  
       foreach (var item in final1)  
       {  
         Console.WriteLine("----" + item.Key + "-----");  
         foreach (var item1 in item.List)  
         {  
           Console.WriteLine(item1.id);  
           Console.WriteLine(item1.name);  
           Console.WriteLine();  
         }  
       }  
       Console.ReadLine();  
     }  
   }  
 }  

Both Gives Same result: 

Group By and Sum

Code

using System;  
 using System.Collections.Generic;  
 using System.Linq;  
 namespace LINQ  
 {  
   class Program  
   {  
     public class student  
     {  
       public int id { get; set; }  
       public string name { get; set; }  
       public int classId { get; set; }  
       public int Salary { get; set; }  
       public List<student> getStudents()  
       {  
         List<student> obj = new List<student>();  
         obj.Add(new student { id = 101, name = "abc1", classId = 1, Salary = 100 });  
         obj.Add(new student { id = 102, name = "abc2", classId = 1, Salary = 200 });  
         obj.Add(new student { id = 103, name = "abc3", classId = 2, Salary = 300 });  
         obj.Add(new student { id = 104, name = "abc4", classId = 2, Salary = 800 });  
         obj.Add(new student { id = 105, name = "abc5", classId = 2, Salary = 900 });  
         obj.Add(new student { id = 106, name = "abc6", classId = 3, Salary = 250 });  
         obj.Add(new student { id = 107, name = "abc7", classId = 3, Salary = 260 });  
         obj.Add(new student { id = 108, name = "abc8", classId = 3, Salary = 290 });  
         return obj;  
       }  
     }  
     static void Main(string[] args)  
     {  
       student s = new student();  
       var students = s.getStudents().ToList();  
       var z = students.GroupBy(x => x.classId).Select(g => new {ClassId=g.Key, TotalSalary= g.Sum(x=>x.Salary) });  
       foreach (var item in z)  
       {  
         Console.WriteLine(item.ClassId);  
         Console.WriteLine(item.TotalSalary);  
         Console.WriteLine();  
       }  
       Console.ReadLine();  
     }  
   }  
 }  

O/P:

using System;  
 using System.Collections.Generic;  
 using System.Linq;  
 namespace LINQ  
 {  
   class Program  
   {  
     class Parent  
     {  
       public int Id { get; set; }  
       public string Val { get; set; }  
     }  
     class Child  
     {  
       public int Id { get; set; }  
       public string ChildVal { get; set; }  
     }  
     static void Main(string[] args)  
     {  
       List<Parent> plist = new List<Parent>() {  
         new Parent{ Id=1, Val="X"},  
         new Parent{ Id=2, Val="Y"},  
         new Parent{ Id=3, Val="Z"}  
       };  
       List<Child> clist = new List<Child>() {  
         new Child{ Id=1, ChildVal="X1"},  
         new Child{ Id=1, ChildVal="X2"},  
         new Child{ Id=1, ChildVal="X3"},  
         new Child{ Id=2, ChildVal="Y1"},  
         new Child{ Id=2, ChildVal="Y2"},  
         new Child{ Id=4, ChildVal="Y3"},  
       };  
       var joinedResult = from p in plist  
                 join c in clist on p.Id equals c.Id  
             select new { p.Val, c.ChildVal };  
       Console.WriteLine("===JOIN===");  
       foreach (var item in joinedResult)  
       {  
         Console.WriteLine(item.Val);  
         Console.WriteLine(item.ChildVal);  
         Console.WriteLine();  
       }  
       Console.WriteLine("===GROUPJOIN===");  
       var y = from p in plist  
           join c in clist on p.Id equals c.Id into g  
           select new { Parent = p, Children = g };  
       foreach (var item in y)  
       {  
         Console.WriteLine(item.Parent.Id);  
         foreach (var item1 in item.Children)  
         {  
           Console.WriteLine(item1.ChildVal);  
         }  
         Console.WriteLine();  
       }  
       Console.ReadLine();  
     }  
   }  
 }  

Second Highest Salary using LINQ

Topic

Finding the Second Highest or nth highest using Linq

Scenario

• List of Students. Each having name,Salary etc
• Find the second highest or nth highest salary

Code

using System;  
 using System.Collections.Generic;  
 using System.Linq;  
 namespace XML  
 {  
   class Program  
   {  
     public class student  
     {  
       public int id { get; set; }  
       public string name { get; set; }  
       public int classId { get; set; }  
       public int Salary { get; set; }  
       public List<student> getStudents()  
       {  
         List<student> obj = new List<student>();  
         obj.Add(new student { id = 101, name = "abc1", classId = 1, Salary = 100 });  
         obj.Add(new student { id = 102, name = "abc2", classId = 1, Salary = 200 });  
         obj.Add(new student { id = 103, name = "abc3", classId = 2, Salary = 300 });  
         obj.Add(new student { id = 104, name = "abc4", classId = 2, Salary = 800 });  
         obj.Add(new student { id = 105, name = "abc5", classId = 2, Salary = 900 });  
         obj.Add(new student { id = 106, name = "abc6", classId = 3, Salary = 250 });  
         obj.Add(new student { id = 107, name = "abc7", classId = 3, Salary = 260 });  
         obj.Add(new student { id = 108, name = "abc8", classId = 3, Salary = 290 });  
         return obj;  
       }  
     }  
     static void Main(string[] args)  
     {  
       student s = new student();  
       var students = s.getStudents().ToList();  
       var firsthighest = students.OrderByDescending(x => x.Salary).Select(x => x.Salary).First();  
       var secondhighest = students.OrderByDescending(x => x.Salary).Where(x => x.Salary != firsthighest).Select(x => x.Salary).First();  
       var secondhighest1 = students.OrderByDescending(x => x.Salary).Skip(2).Select(x => x.Salary).First();  
       var secondhighest2 = students.Where(x => x.Salary != (students.Max(x1 => x1.Salary))).Select(x => x.Salary).Max();  
       Console.WriteLine(secondhighest1);  
       Console.WriteLine(secondhighest2);  
       Console.ReadLine();  
     }  
   }  
 }  

Output