Sorting Operators: OrderBy & OrderByDescending
A sorting operator arranges the elements of the collection in ascending or descending order. LINQ includes following sorting operators.
| Sorting Operator | Description |
|---|---|
| OrderBy | Sorts the elements in the collection based on specified fields in ascending or decending order. |
| OrderByDescending | Sorts the collection based on specified fields in descending order. Only valid in method syntax. |
| ThenBy | Only valid in method syntax. Used for second level sorting in ascending order. |
| ThenByDescending | Only valid in method syntax. Used for second level sorting in descending order. |
| Reverse | Only valid in method syntax. Sorts the collection in reverse order. |
OrderBy
OrderBy sorts the values of a collection in ascending or descending order. It sorts the collection in ascending order by default because ascending keyword is optional here. Use descending keyword to sort collection in descending order.
IList<Student> studentList = new List<Student>() {
new Student() { StudentID = 1, StudentName = "John", Age = 18 } ,
new Student() { StudentID = 2, StudentName = "Steve", Age = 15 } ,
new Student() { StudentID = 3, StudentName = "Bill", Age = 25 } ,
new Student() { StudentID = 4, StudentName = "Ram" , Age = 20 } ,
new Student() { StudentID = 5, StudentName = "Ron" , Age = 19 }
};
var orderByResult = from s in studentList
orderby s.StudentName
select s;
var orderByDescendingResult = from s in studentList
orderby s.StudentName descending
select s;Dim orderByResult = From s In studentList
Order By s.StudentName
Select s
Dim orderByDescendingResult = From s In studentList
Order By s.StudentName Descending
Select sorderByResult in the above example would contain following elements after execution:
BillJohn
Ram
Ron
Steve
orderByDescendingResult in the above example would contain following elements after execution:
SteveRon
Ram
John
Bill
OrderBy in Method Syntax
OrderBy extension method has two overloads. First overload of OrderBy extension method accepts the Func delegate type parameter. So you need to pass the lambda expression for the field based on which you want to sort the collection.
The second overload method of OrderBy accepts object of IComparer along with Func delegate type to use custom comparison for sorting.
public static IOrderedEnumerable<TSource> OrderBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector); public static IOrderedEnumerable<TSource> OrderBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, IComparer<TKey> comparer);
The following example sorts the studentList collection in ascending order of StudentName using OrderBy extension method.
IList<Student> studentList = new List<Student>() {
new Student() { StudentID = 1, StudentName = "John", Age = 18 } ,
new Student() { StudentID = 2, StudentName = "Steve", Age = 15 } ,
new Student() { StudentID = 3, StudentName = "Bill", Age = 25 } ,
new Student() { StudentID = 4, StudentName = "Ram" , Age = 20 } ,
new Student() { StudentID = 5, StudentName = "Ron" , Age = 19 }
};
var studentsInAscOrder = studentList.OrderBy(s => s.StudentName);Dim studentsInAscOrder = studentList.OrderBy(Function(s) s.StudentName)
OrderByDescending
OrderByDescending sorts the collection in descending order.
OrderByDescending is valid only with the Method syntax. It is not valid in query syntax because the query syntax uses ascending and descending attributes as shown above.
IList<Student> studentList = new List<Student>() {
new Student() { StudentID = 1, StudentName = "John", Age = 18 } ,
new Student() { StudentID = 2, StudentName = "Steve", Age = 15 } ,
new Student() { StudentID = 3, StudentName = "Bill", Age = 25 } ,
new Student() { StudentID = 4, StudentName = "Ram" , Age = 20 } ,
new Student() { StudentID = 5, StudentName = "Ron" , Age = 19 }
};
var studentsInDescOrder = studentList.OrderByDescending(s => s.StudentName);Dim studentsInDescOrder = studentList.OrderByDescending(Function(s) s.StudentName)A result in the above example would contain following elements after execution.
SteveRon
Ram
John
Bill
Please note that OrderByDescending is not supported in query syntax. Use the decending keyword instead.
Multiple Sorting
You can sort the collection on multiple fields seperated by comma. The given collection would be first sorted based on the first field and then if value of first field would be the same for two elements then it would use second field for sorting and so on.
IList<Student> studentList = new List<Student>() {
new Student() { StudentID = 1, StudentName = "John", Age = 18 } ,
new Student() { StudentID = 2, StudentName = "Steve", Age = 15 } ,
new Student() { StudentID = 3, StudentName = "Bill", Age = 25 } ,
new Student() { StudentID = 4, StudentName = "Ram" , Age = 20 } ,
new Student() { StudentID = 5, StudentName = "Ron" , Age = 19 },
new Student() { StudentID = 6, StudentName = "Ram" , Age = 18 }
};
var orderByResult = from s in studentList
orderby s.StudentName, s.Age
select new { s.StudentName, s.Age };In the above example, studentList collection includes two identical StudentNames, Ram. So now, studentList would be first sorted based on StudentName and then by Age in ascending order. So, orderByResult would contain following elements after execution
StudentName: Bill, Age: 25StudentName: John, Age: 18
StudentName: Ram, Age: 18
StudentName: Ram, Age: 20
StudentName: Ron, Age: 19
StudentName: Steve, Age: 15
Points to Remember :
- LINQ includes five sorting operators: OrderBy, OrderByDescending, ThenBy, ThenByDescending and Reverse
- LINQ query syntax does not support OrderByDescending, ThenBy, ThenByDescending and Reverse. It only supports 'Order By' clause with 'ascending' and 'descending' sorting direction.
- LINQ query syntax supports multiple sorting fields seperated by comma whereas you have to use ThenBy & ThenByDescending methods for secondary sorting.
