Comparison between IComparer and IComparable in CSharp
I’ve already written an article introducing the usage of comparer here. In this article I’ll compare the usage of IComparable and IComparer with examples.
Important difference: A class can have only one Comparable, but multiple Comparers.
Here I have a class Student with different properties, which will be used as sorting criterias.
public class Student : IComparable<Student>
{
public string LastName { get; set; }
public string FirstName { get; set; }
public int Age { get; set; }
public int Class { get; set; }
}
Firstly, I want class Student to implement interface IComparable, and I must override method CompareTo of interface IComparable. In this method I sort Student list in an ascending order.
//class who implement interface IComparable, must implement CompareTo method
public class Student : IComparable<Student>
{
public string LastName { get; set; }
public string FirstName { get; set; }
public int Age { get; set; }
public int Class { get; set; }
//CompareTo method compare itself to another object
public int CompareTo(Student student)
{
return LastName.CompareTo(student.LastName);
}
}
In this way, Student list will be sorted by LastName in an ascending order.
Next, I’ll create 3 comparers who will use the rest 3 properties as sorting criteria.
//Comparer 1
//class who implement interfce IComparer, must implement Compare method
public class OrderByAgeAscending : IComparer<Student>
{
//Compare method compares two objects
public int Compare(Student x, Student y)
{
if (x.Age.CompareTo(y.Age) < 0)
{
return -1;
}
if (x.Age.CompareTo(y.Age) == 0)
{
return 0;
}
return 1;
}
}
//Comparer 2
public class OrderByClassDescending : IComparer<Student>
{
public int Compare(Student x, Student y)
{
if (x.Class.CompareTo(y.Class) < 0)
{
return 1;
}
if (x.Class.CompareTo(y.Class) == 0)
{
return 0;
}
return -1;
}
}
//Comparer 3
public class OrderByFirstNameAscending : IComparer<Student>
{
public int Compare(Student x, Student y)
{
if (x.FirstName.CompareTo(y.FirstName) < 0)
{
return -1;
} if (x.FirstName.CompareTo(y.FirstName) == 0)
{
return 0;
}
return 1;
}
}
Now I will create a new Student list with some Students and try to sort them with comparable and comparer. Firstly, I will create a list.
var s1 = new Student() { LastName = "charles", FirstName = "charles", Age = 27, Class = 15 };
var s2 = new Student() { LastName = "viz", FirstName = "newton", Age = 20, Class = 30 };
var s3 = new Student() { LastName = "la", FirstName = "aba", Age = 2, Class = 2 };
var students = new List<Student>() { s1, s2, s3 };
Then, I will sort the list with comparable. I just need to call Sort() method, it will use the CompareTo() method I’ve created.
//IComparable: sort by last name
students.Sort();
Display(students, "IComparable OrderByLastName:");
And then, I will use the 3 comparers to sort the list.
//Comparer 1: order by age
var c1 = new OrderByAgeAscending();
students.Sort(c1);
Display(students, "Comparer OrderByAgeAscending:");
//Comparer 2: order by class
var c2 = new OrderByClassDescending();
students.Sort(c2);
Display(students, "Comparer OrderByClassDescending:");
//Comparer 3: order by first name
var c3 = new OrderByFirstNameAscending();
students.Sort(c3);
Display(students, "Comparer OrderByFirstNameAscending");
And there are an Display() method who is in charge of display the student information.
public static void Display(List<Student> students, string comparerName)
{
Console.WriteLine(comparerName);
foreach (var student in students)
{
Console.WriteLine("last name: " + student.LastName + "; first name: " + student.FirstName + "; age: " + student.Age + "; class: " + student.Class);
}
}
Now, let’s see the results:
Right now, we are arrived at the end of the article. I hope you can find useful information here. Enjoy coding!
