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Part 18 - GroupBy in LINQ

Suggested Videos
Part 15 - Conversion Operators in LINQ
Part 16 - Cast and OfType operators in LINQ
Part 17 - AsEnumerable and AsQueryable in LINQ



GroupBy operator belong to Grouping Operators category. This operator takes a flat sequence of items, organize that sequence into groups (IGrouping<K,V>) based on a specific key and return groups of sequences. 



In short, GroupBy creates and returns a sequence of IGrouping<K,V>

Let us understand GroupBy with examples.

We will use the following Employee class in this demo
public class Employee
{
    public int ID { get; set; }
    public string Name { get; set; }
    public string Gender { get; set; }
    public string Department { get; set; }
    public int Salary { get; set; }

    public static List<Employee> GetAllEmployees()
    {
        return new List<Employee>()
        {
            new Employee { ID = 1, Name = "Mark", Gender = "Male",
                                         Department = "IT", Salary = 45000 },
            new Employee { ID = 2, Name = "Steve", Gender = "Male",
                                         Department = "HR", Salary = 55000 },
            new Employee { ID = 3, Name = "Ben", Gender = "Male",
                                         Department = "IT", Salary = 65000 },
            new Employee { ID = 4, Name = "Philip", Gender = "Male",
                                         Department = "IT", Salary = 55000 },
            new Employee { ID = 5, Name = "Mary", Gender = "Female",
                                         Department = "HR", Salary = 48000 },
            new Employee { ID = 6, Name = "Valarie", Gender = "Female",
                                         Department = "HR", Salary = 70000 },
            new Employee { ID = 7, Name = "John", Gender = "Male",
                                         Department = "IT", Salary = 64000 },
            new Employee { ID = 8, Name = "Pam", Gender = "Female",
                                         Department = "IT", Salary = 54000 },
            new Employee { ID = 9, Name = "Stacey", Gender = "Female",
                                         Department = "HR", Salary = 84000 },
            new Employee { ID = 10, Name = "Andy", Gender = "Male",
                                         Department = "IT", Salary = 36000 }
        };
    }
}

Example 1: Get Employee Count By Department
var employeeGroup = from employee in Employee.GetAllEmployees()
                    group employee by employee.Department;

foreach (var group in employeeGroup)
{
    Console.WriteLine("{0} - {1}", group.Key, group.Count());
}

Output:
linq group by

Example 2: Get Employee Count By Department and also each employee and department name
var employeeGroup = from employee in Employee.GetAllEmployees()
                                      group employee by employee.Department;

foreach (var group in employeeGroup)
{
    Console.WriteLine("{0} - {1}", group.Key, group.Count());
    Console.WriteLine("----------");
    foreach (var employee in group)
    {
        Console.WriteLine(employee.Name + "\t" + employee.Department);
    }
    Console.WriteLine(); Console.WriteLine();
}

Output:
linq group by example

Example 3: Get Employee Count By Department and also each employee and department name. Data should be sorted first by Department in ascending order and then by Employee Name in ascending order.
var employeeGroup = from employee in Employee.GetAllEmployees()
                                      group employee by employee.Department into eGroup
                                      orderby eGroup.Key
                                      select new
                                      {
                                           Key = eGroup.Key,
                                           Employees = eGroup.OrderBy(x => x.Name)
                                      };

foreach (var group in employeeGroup)
{
    Console.WriteLine("{0} - {1}", group.Key, group.Employees.Count());
    Console.WriteLine("----------");
    foreach (var employee in group.Employees)
    {
        Console.WriteLine(employee.Name + "\t" + employee.Department);
    }
    Console.WriteLine(); Console.WriteLine();
}

Output:
groupby linq c# example

linq tutorial

3 comments:

  1. PLease how to convert this expression into lambda expression
    var employeeGroup = from employee in Employee.GetAllEmployees()
    group employee by employee.Department into eGroup
    orderby eGroup.Key
    select new
    {
    Key = eGroup.Key,
    Employees = eGroup.OrderBy(x => x.Name)
    };

    ReplyDelete
    Replies
    1. Employee.GetAllEmployees().GroupBy(x => x.Department).OrderBy(c => c.Key)
      .Select(x => new
      {
      Key=x.Key,
      employee = x.OrderBy(c => c.Name)
      });

      check more on csharphy.blogpost.in

      Delete
    2. var result = Employee.GetAll().GroupBy(g => g.Department).Select(p => new {Department = p.Key,Person=p});
      foreach (var item in result)
      {
      Console.WriteLine("Department : {0}",item.Department);
      Console.WriteLine();
      foreach (var person in item.Person)
      {

      Console.WriteLine("ID : {0}", person.ID);
      Console.WriteLine("Name : {0}", person.Name);
      Console.WriteLine("Gender : {0}", person.Gender);
      Console.WriteLine("Salary : {0}", person.Salary);
      Console.WriteLine("Department : {0}", person.Department);
      Console.WriteLine();
      }

      Check my Blog :www.cfetch.blogspot.com For more..

      Delete

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