Objective
In this article, I am going to show, how we could achieve filtering and sorting in LINQ to object
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 { |
Hostel.cs
| namespace LINQtoOBJECT1 { public class Hostel |
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 }, |
Function to return collection of hostels
| static List<Hostel> GetHostel(){
List<Hostel> hostels = new List<Hostel> |
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.
Filtering in LINQ
In below code, I am filtering result. I am only fetching detail of student with RollNumber 1.
List<Student> lstStudents = GetStudents(); Student student = (from r in lstStudents where r.RollNumber == 1 select r).First(); Console.WriteLine(student.Name + student.RollNumber + student.HostelNumber + student.Section); |
If you see closely in above LINQ query, I am using First clause. Because if I am returning the output in a Student type and default return type of LINQ is IEnumerable. If I modify the above LINQ as below
| Student student = (from r in lstStudents where r.RollNumber == 1 select r); |
At compile time we can expect below error,
When we run the above code
Output
Now if I want to have, named of all the students whose roll number is more than 3 and who resides in hostel number 2.
| List<Student> lstStudents = GetStudents(); IEnumerable<string> lstStudentName = from r in lstStudents where r.RollNumber > 3 && r.HostelNumber==2 foreach (string name in lstStudentName) |
In above LINQ query, I am applying both filtering and projection.
Output
Intermediate values
If I want to have intermediate values in my LINQ query then LET clause come into action. LET clause helps to reduce redundancy in WHERE clause.
| IEnumerable<string> lstStudentName = from r in lstStudents let condition = r.RollNumber where condition > 3 && r.HostelNumber== 2 select r.Name ; |
Let clause can be having complex statements.
Sorting in LINQ
OrderBy clause is used for purpose of sorting in LINQ.
Sorting a single property
Just before WHERE clause, OrederBy clause is used to sort the query result. In code Name of the students will be displayed in ascending order.
| List<Student> lstStudents = GetStudents(); IEnumerable<string> lstStudentName = from r in lstStudents let condition = r.RollNumber orderby r.Name where condition > 3 && r.HostelNumber== 2 select r.Name ; foreach (string name in lstStudentName) Console.WriteLine(name); |
Output
Sorting multiple properties
By putting comma between properties multiple properties can be sorted. Sorting will be done left to right. For roll number property I am sorting in descending order. This can be achieved by using keyword DESCENDIG. By default sorting is ascending.
List<Student> lstStudents = GetStudents(); IEnumerable<Student> lstStudentName = from r in lstStudents let condition = r.RollNumber orderby r.Name,r.RollNumber descending foreach (Student name in lstStudentName) Console.WriteLine(name.RollNumber + name.Name); |
Conclusion
In next part, I will be explaining Grouping. I hope this article was useful to you. Thanks for reading.
Dhananjay Kumar 
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