LINQ to Object Part #3: Grouping

Objective

In this article, I am going to show, how we could achieve grouping in LINQ to object, Here is the Second Part.

I have created two classes for my explanation purpose. Student class is having details of students and Hostel class is having details of hostel. Both classes are having a properties HostelNumber common. I will be using this property to perform join operations in later articles. Both classes are as below.
 
Student.cs

namespace LINQtoOBJECT1
{
     public  class Student
    {

         public int RollNumber { get; set; }
         public string Name { get; set; }
         public int Section { get; set; }
         public int HostelNumber { get; set; }
    }
}

Hostel.cs

namespace LINQtoOBJECT1
{
   public class Hostel
    {

       public int HostelNumber { get; set; }
       public int NumberofRooms { get; set; }
    }
}

To create collection of students and hostels, I am creating two static functions.

Function to return collection of students

static List<Student> GetStudents()
        {
            List<Student> students = new List<Student>
            {
                new Student() { RollNumber = 1,Name ="Alex " , Section = 1 ,HostelNumber=1 },
                new Student() { RollNumber = 2,Name ="Jonty " , Section = 2 ,HostelNumber=2 },
                new Student() { RollNumber = 3,Name ="Samba " , Section = 3 ,HostelNumber=1 },
                new Student() { RollNumber = 4,Name ="Donald " , Section = 3 ,HostelNumber=2 },
                new Student() { RollNumber = 5,Name ="Kristen " , Section = 2 ,HostelNumber=1 },
                new Student() { RollNumber = 6,Name ="Mark " , Section = 1 ,HostelNumber=2},
                new Student() { RollNumber = 7,Name ="Gibbs " , Section = 1 ,HostelNumber=1 },
                new Student() { RollNumber = 8,Name ="Peterson " , Section = 2 ,HostelNumber=2 },
                new Student() { RollNumber = 9,Name ="collingwood " , Section = 3 ,HostelNumber=1 },
                new Student() { RollNumber = 10,Name ="Brian " , Section = 3 ,HostelNumber=2 }

            };

            return students;
        }

Function to return collection of hostels

static List<Hostel> GetHostel()
        {
            List<Hostel> hostels = new List<Hostel>
            {

                new Hostel(){HostelNumber=1 ,NumberofRooms = 100},
                new Hostel(){HostelNumber= 2 ,NumberofRooms = 200}
            };
            return hostels;
        }

Now have a look on both codes below, one is using LINQ and other is using LOOP to retrieve data from the list and print.

Note: I will be using above two classes and functions for my entire sample below.

Grouping in LINQ



Syntax of Groupby

Var result  = FROM  selectVariable IN  dataSourceorList GROUPBY selectVariable.variable INTO RANGEVARIABLE Select new { };

Grouping by a single property

List<Student> lstStudents = GetStudents();
          var  lstStudentName = from r in lstStudents
                                                   group r by r.HostelNumber into   rngStudent
                                                   select new
                                                   {
                                                       HostelID = rngStudent.Key,
                                                       Students = rngStudent
                                                   };

          foreach (var name in lstStudentName)
          {
              Console.WriteLine(name.HostelID);
              foreach (Student s in name.Students)
              {
                  Console.WriteLine(s.RollNumber + s.Name);
              }
          }
             Console.ReadKey();

Explanation

1. I am grouping on property hostel number.
2. rngStudent is range variable in which ; I am putting the intermediate result.
3. I am selecting the result in as anonymous type.
4. While printing the result , first I am printing the key of group by and then retrieving the object in foreach.

Output



Accessing the Group object

foreach (var name in lstStudentName)
          {
              Console.WriteLine(name.HostelID);
              foreach (Student s in name.Students)
              {
                  Console.WriteLine(s.RollNumber + s.Name);
              }
          }

If you see the above loop , first I am looping the key for the group by clause and then , I am looping through IEnumerable LINQ object. This object is containing the real result.

Conclusion

In this article, I have discussed GROUPING in LINQ to OBJECT. Thanks for reading.