Using IComparable in C#

In case you want to compare 2 objects for sorting purpose you can use this interface. IComparable defines a type specific comparison method. Value types and classes can implement this interface. 

Lets say you have a list of people and you want to sort it by age. You'll use Sort method comes with the list. Usually the Sort() method will use default comparer for the type specified by the generic argument, Here default comparer for Person. 

	public class Program
	{
	static void Main(string[] args)
	{
	Person p1 = new Person() { Name = "Person 1", Age = 34 };
	Person p2 = new Person() { Name = "Person 2", Age = 31 };
	Person p3 = new Person() { Name = "Person 3", Age = 33 };
	Person p4 = new Person() { Name = "Person 4", Age = 26 };
	List<Person> people = new List<Person> { p1, p2, p3, p4 };
	//Exception : Failed to compare two elements in the array
	people.Sort();
	}
	}
	public class Person
	{
	public string Name { get; set; }
	public int Age { get; set; }
	}

view raw list_sort1.cs hosted with ❤ by GitHub

But it'll throw an error when trying to sort because Person does not have a comparer and it does not know how to sort them. Therefore you need to implement IComparable and its CompareTo method like below.

	public class Person : IComparable
	{
	public string Name { get; set; }
	public int Age { get; set; }
	public int CompareTo(Object obj)
	{
	Person otherPerson = obj as Person;
	if (otherPerson == null)
	{
	throw new ArgumentNullException();
	}
	else
	{
	return Age.CompareTo(otherPerson.Age);
	}
	}
	}

view raw person_icomparable.cs hosted with ❤ by GitHub

Now the sorting will happen successfully. Note that implementation of CompareTo(Object) must return a Int32. All numeric types such as Int32 and Double implements IComparable.

Resources

MSDN Documentation

http://www.dotnetperls.com/icomparable

http://stackoverflow.com/questions/538096/when-to-use-icomparablet-vs-icomparert

http://stackoverflow.com/questions/2488298/advantages-disadvantages-of-different-implementations-for-comparing-objects

http://stackoverflow.com/questions/27689085/generically-compare-two-objects

http://stackoverflow.com/questions/6480577/c-sharp-generics-how-to-compare-values-of-generic-types?lq=1

http://stackoverflow.com/questions/506096/comparing-object-properties-in-c-sharp?rq=1