C# Sort KeyValuePair List

KeyValuePair: Key and Value properties

A List contains many KeyValuePair struct instances. It can be sorted with the Sort List method. This requires Comparison delegate implementations. We implement these as static int methods that call CompareTo.

ComparisonCompareTo

Example

Main method

This example code introduces three static methods. Compare1 receives two KeyValuePair structs and returns the result of CompareTo on their Key. Compare2 returns the CompareTo of the Value. And in the Main entry point control flow begins.

KeyValuePairMain, Args
C# program that sorts List of KeyValuePair instances

using System;
using System.Collections.Generic;

class Program
{
    static int Compare1(KeyValuePair<string, int> a, KeyValuePair<string, int> b)
    {
	return a.Key.CompareTo(b.Key);
    }

    static int Compare2(KeyValuePair<string, int> a, KeyValuePair<string, int> b)
    {
	return a.Value.CompareTo(b.Value);
    }

    static void Main()
    {
	var list = new List<KeyValuePair<string, int>>();
	list.Add(new KeyValuePair<string, int>("Perl", 7));
	list.Add(new KeyValuePair<string, int>("Net", 9));
	list.Add(new KeyValuePair<string, int>("Dot", 8));

	// Use Compare1 as comparison delegate.
	list.Sort(Compare1);

	foreach (var pair in list)
	{
	    Console.WriteLine(pair);
	}
	Console.WriteLine();

	// Use Compare2 as comparison delegate.
	list.Sort(Compare2);

	foreach (var pair in list)
	{
	    Console.WriteLine(pair);
	}
    }
}

Output

[Dot, 8]
[Net, 9]
[Perl, 7]

[Perl, 7]
[Dot, 8]
[Net, 9]
List type

In this example, a new List of KeyValuePair instances is created. Three KeyValuePairs are created and added to the List. Next the List is sorted with Compare1. The method target Compare1 is accepted as a Comparison delegate.

Then:After printing the List, we sort it again with Compare2, and finally display the List again.

ListConsole.WriteLineSorted letters: A to Z

The results reveal the effects of the Comparison delegates. The List.Sort(Compare1) call sorts the List by the Key of the KeyValuePair. And the List.Sort(Compare2) call sorts the List by the Value int.

Sort List

Summary

With this example program, we implemented one way of sorting collections of KeyValuePair instances. You can use other syntax forms and implementations, such as LINQ expressions or lambda expressions, to accomplish this task as well.

orderbyLambda Expression

C#: Sort