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  • Grouping Operators in Linq

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    Grouping operators generates a categories or groups of an item on the basis of given key. These type of operators implements IEnumerable collection of type IGrouping<Key, SourceItem> where Key is a key value, on the basis of which grouping is being done and SourceItem is the collection of items.

    In linq, We have a two types of grouping operators:
    1. GroupBy
    2. ToLookup

    1. GroupBy:- It takes a collection of items and returns  a group of items from the given collection based on some key value.


    Query syntax :-
    Lets take an example we have a collection of an employees of a different departments. We need to make a groups of an employee of a same department.


    Code:-

    IList<Employee> empList = new List<Employee>() { 
            new Employee() { EmpID = Guid.NewGuid().ToString(), EmpName = "John", Dept = "Electronic Department" } ,
            new Employee() { EmpID = Guid.NewGuid().ToString(), EmpName = "Steve",  Dept = "Computer Department" } ,
            new Employee() { EmpID = Guid.NewGuid().ToString(),  EmpName = "Bill",  Dept = "Geographical Department" } ,
            new Employee() { EmpID = Guid.NewGuid().ToString(), EmpName = "Ram" , Dept = "Computer Department" } ,
            new Employee() { EmpID = Guid.NewGuid().ToString(),  EmpName = "Abram" , Dept = "Geographical Department" } 
        };
    var result = from e in empList 
                        group e by e.Dept;
    foreach (var deptGroup in result)
    {
        Console.WriteLine("Department Group: {0}", deptGroup .Key); 
        foreach(Employee e in deptGroup ) 
         {
               Console.WriteLine("Employee Name: {0}", e.EmpName);
          }
    }
    

     

    Output:-

     

    Method syntax for above code:-

    IList<Employee> empList = new List<Employee>() {
            new Employee() { EmpID = Guid.NewGuid().ToString(), EmpName = "John", Dept = "Electronic Department" } ,
            new Employee() { EmpID = Guid.NewGuid().ToString(), EmpName = "Steve",  Dept = "Computer Department" } ,
            new Employee() { EmpID = Guid.NewGuid().ToString(), EmpName = "Bill",  Dept = "Geographical Department" } ,
            new Employee() { EmpID = Guid.NewGuid().ToString(), EmpName = "Ram" , Dept = "Computer Department" } ,
            new Employee() { EmpID = Guid.NewGuid().ToString(), EmpName = "Abram" , Dept = "Geographical Department" }
        };
             var result = empList .GroupBy(e => e.Dept);
                foreach (var deptGroup in result)
                {
                    Console.WriteLine("Department Group: {0}", deptGroup.Key);
                    foreach (Employee e in deptGroup)
                    {
                        Console.WriteLine("Employee Name: {0}", e.EmpName);
                    }
                }
    

     

    2.  ToLookup:-
    ToLookup operator is similar to a GroupBy operator but their execution way is different because GroupBy operator executes delay while ToLookup operator executes instantly. ToLookup also not supports a query syntax, it supports only a method syntax.


    Example:-
    Let's take an example, we have a collection of employees of a different departments. We need to make a group of an employee of a same department.


    Code:-

    IList<Employee> empList = new List<Employee>() {
            new Employee() { EmpID = Guid.NewGuid().ToString(), EmpName = "John", Dept = "Electronic Department" } ,
            new Employee() { EmpID = Guid.NewGuid().ToString(), EmpName = "Steve",  Dept = "Computer Department" } ,
            new Employee() { EmpID = Guid.NewGuid().ToString(), EmpName = "Bill",  Dept = "Geographical Department" } ,
            new Employee() { EmpID = Guid.NewGuid().ToString(), EmpName = "Ram" , Dept = "Computer Department" } ,
            new Employee() { EmpID = Guid.NewGuid().ToString(), EmpName = "Abram" , Dept = "Geographical Department" }
        };
             var result = empList .ToLookup(e=>e.Dept);
                foreach (var deptGroup in result)
                {
                    Console.WriteLine("Department Group: {0}", deptGroup.Key);
                    foreach (Employee e in deptGroup)
                    {
                        Console.WriteLine("Employee Name: {0}", e.EmpName);
                    }
                }
    

     

    Output:-

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