Projection Operators: Select, SelectMany

There are two projection operators available in LINQ. 1) Select 2) SelectMany

Select

The Select operator always returns an IEnumerable collection which contains elements based on a transformation function. It is similar to the Select clause of SQL that produces a flat result set.

Now, let's understand Select query operator using the following Student class.

public class Student{ 
    public int StudentID { get; set; }
    public string StudentName { get; set; }
    public int Age { get; set; }
}

Try it

Select in Query Syntax

LINQ query syntax must end with a Select or GroupBy clause. The following example demonstrates select operator that returns a string collection of StudentName.

Example: Select in Query Syntax C#

IList<Student> studentList = new List<Student>() { 
    new Student() { StudentID = 1, StudentName = "John" },
    new Student() { StudentID = 2, StudentName = "Moin" },
    new Student() { StudentID = 3, StudentName = "Bill" },
    new Student() { StudentID = 4, StudentName = "Ram" },
    new Student() { StudentID = 5, StudentName = "Ron" } 
};

var selectResult = from s in studentList
                   select s.StudentName;

Try it

The select operator can be used to formulat the result as per our requirement. It can be used to return a collection of custom class or anonymous type which includes properties as per our need.

The following example of the select clause returns a collection of anonymous type containing the Name and Age property.

Example: Select in Query Syntax C#

IList<Student> studentList = new List<Student>() { 
    new Student() { StudentID = 1, StudentName = "John", Age = 13 } ,
    new Student() { StudentID = 2, StudentName = "Moin",  Age = 21 } ,
    new Student() { StudentID = 3, StudentName = "Bill",  Age = 18 } ,
    new Student() { StudentID = 4, StudentName = "Ram" , Age = 20 } ,
    new Student() { StudentID = 5, StudentName = "Ron" , Age = 15 } 
};

// returns collection of anonymous objects with Name and Age property
var selectResult = from s in studentList
                   select new { Name = "Mr. " + s.StudentName, Age = s.Age }; 

// iterate selectResult
foreach (var item in selectResult)
    Console.WriteLine("Student Name: {0}, Age: {1}", item.Name, item.Age);

Try it

Output:

Student Name: Mr. John, Age: 13 Student Name: Mr. Moin, Age: 21 Student Name: Mr. Bill, Age: 18 Student Name: Mr. Ram, Age: 20 Student Name: Mr. Ron, Age: 15

Select in Method Syntax

The Select operator is optional in method syntax. However, you can use it to shape the data. In the following example, Select extension method returns a collection of anonymous object with the Name and Age property:

Example: Select in Method Syntax C#

IList<Student> studentList = new List<Student>() { 
    new Student() { StudentID = 1, StudentName = "John", Age = 18 } ,
    new Student() { StudentID = 2, StudentName = "Moin",  Age = 21 } ,
    new Student() { StudentID = 3, StudentName = "Bill",  Age = 18 } ,
    new Student() { StudentID = 4, StudentName = "Ram" , Age = 20 } ,
    new Student() { StudentID = 5, StudentName = "Ron" , Age = 21 } 
};
    
var selectResult = studentList.Select(s =&gt; new { Name = s.StudentName , 
                                                 Age = s.Age  });

Try it

In the above example, selectResult would contain anonymous objects with Name and Age property as shown below in the debug view.

Select clause returns an Anonymous objects

Select Many

The SelectMany operator projects sequences of values that are based on a transform function and then flattens them into one sequence.

Visit MSDN for more information on projection operators.