Thursday, December 25, 2008

6:44 AM

By Kannan

In: , , ,

C# array in descending or reverse order

How do you sort a C# array in descending or reverse order? A simple way is to sort the array in ascending order, then reverse it:
int[] intArray = new int[] { 3, 1, 4, 5, 2 };
Array.Sort<int>( intArray );
Array.Reverse( intArray );
Of course, this is not efficient for large arrays.

A better approach is to create a custom Comparer. Following is a nice generics class that will sort an array in descending order. Note that the object type must be comparable (inherit from IComparable) as any useful class should.

Here’s a simple web application to test it:

<%@ Page Language="C#" AutoEventWireup="true" Codebehind="SortSample.aspx.cs" Inherits="SampleApplication.SortSample" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Sort Ascending /Descending Order by Generic</title>
</head>
<body>
    <form id="form1" runat="server">
        <div>
            <asp:DropDownList ID="DropDownList1" runat="server">
            </asp:DropDownList>
            <asp:DropDownList ID="DropDownList2" runat="server">
            </asp:DropDownList>
            <asp:DropDownList ID="DropDownList3" runat="server">
            </asp:DropDownList>
        </div>
    </form>
</body>
</html>
using System;
using System.Collections.Generic;
using System.Web.UI.WebControls;

namespace SampleApplication.
{
    public partial class SortSample: System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            int[] intArray = new int[] { 3, 1, 4, 5, 2 };
            char[] charArray = new char[] { 'r', '1', 'f', 'c', 'x' };
            string[] stringArray = new string[] { "array item 1", "array item 2", "array item 3", "array item 4", "array item 5" };

            ArraySorter<int>.SortDescending(intArray);
            ArraySorter<char>.SortDescending(charArray);
            ArraySorter<string>.SortDescending(stringArray);
         
            BindDropDownList(DropDownList1, intArray);
            BindDropDownList(DropDownList2, charArray);
            BindDropDownList(DropDownList3, stringArray);
        }

        private static void BindDropDownList(BaseDataBoundControl ddl, Array arr)
        {
            if(ddl !=null && arr !=null && arr.Length>0)
            {
                ddl.DataSource = arr;
                ddl.DataBind();
            }
        }
        static public class ArraySorter<T> where T : IComparable
        {
            static public void SortDescending(T[] array)
            {
                Array.Sort<T>(array, s_Comparer);
            }

            static private readonly ReverseComparer s_Comparer = new ReverseComparer();

            private class ReverseComparer : IComparer<T>
            {
                public int Compare(T object1, T object2)
                {
                    return -((IComparable)object1).CompareTo(object2);
                }
            }
        }

    }
}

I hope it will help you in someway.

Happy Coding!!!