Sorting an array using an independent Comparer method

Oct. 25, 2017

Introduction

One apple a day, keep doctor away. One program a day, also keep programmer awake. Today a small program keeps me awake to look into a few things, IComparer vs IComparable. 

I like to share my practice using C# 2000 things, item 137: Sorting an array using an independent Comparer method.

Here is the C# code.

Read the code and enjoy the workout.

	using System;
	using System.Collections;
	using System.Collections.Generic;
	using System.Linq;
	using System.Text;
	using System.Threading.Tasks;
	namespace Item137_Sort
	{
	/// <summary>
	/// C# 2000 things
	/// https://csharp.2000things.com/2010/11/01/137-sorting-an-array-using-an-independent-comparer-method/
	/// #137 – Sorting an Array Using an Independent Comparer Method
	/// Instead of extending a type to implement IComparable to allow sorting, you can create a separate class
	/// that knows how to compare objects of that type and use the new class to do the sorting.
	///
	/// Here’s an example of sorting objects of type Person using a custom Compare method. To start with,
	/// we define a new class that implements IComparer.
	/// </summary>
	class Person
	{
	public string FirstName { get; set; }
	public string LastName { get; set; }
	public Person(string firstName, string lastName)
	{
	FirstName = firstName;
	LastName = lastName;
	}
	}
	/// <summary>
	///
	/// </summary>
	public class PersonSorter : IComparer
	{
	public int Compare(object o1, object o2)
	{
	Person p1 = o1 as Person;
	Person p2 = o2 as Person;
	// Sort by LastName, then by FirstName (ignore case)
	int compare = p1.LastName.ToLower().CompareTo(p2.LastName.ToLower());
	if (compare == 0)
	{
	compare = p1.FirstName.ToLower().CompareTo(p2.FirstName.ToLower());
	}
	return compare;
	}
	}
	class Program
	{
	/// <summary>
	/// Now we can sort using this compare function by passing an instance of the IComparer
	/// class into the Sort method.
	/// </summary>
	/// <param name="args"></param>
	static void Main(string[] args)
	{
	Person[] folks = new Person[4];
	folks[0] = new Person("Bronte", "Emily");
	folks[1] = new Person("Bronte", "Charlotte");
	folks[2] = new Person("Tennyson", "Alfred");
	folks[3] = new Person("Mailer", "Norman");
	Array.Sort(folks, new PersonSorter());
	}
	}
	}

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