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Let's randomize IEnumerable

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4.75/5 (4 votes)
9 Oct 2011CPOL 25K   2   6
I needed to randomize a collection. Here's my solution.
I needed to randomize an enumerable collection. Here's what I came up with in the 60 seconds I thought it deserved.

Your challenge:

  1. Do it better. better = faster with same number of items and/or faster with n items.

  2. Prove it.

using System;
using System.Collections.Generic;

/// <summary>
/// Extension class for IEnumerable&lt;T&gt;
/// </summary>
static class IEnumerableExtension
    /// <summary>
    /// Randomizes the specified collection.
    /// </summary>
    /// <typeparam name="T">The type of the collection.</typeparam>
    /// <param name="collection">The collection.</param>
    /// <returns>The randomized collection</returns>
    public static IEnumerable<T> Randomize<T>(this IEnumerable<T> collection)
        // Put all items into a list.
        var list = new List<T>(collection);
        var randomizer = new Random();
        // And pluck them out randomly.
        for (int i = list.Count; i > 0; i--)
            int r = randomizer.Next(0, i);
            yield return list[r];


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Written By
Engineer Robotic Assistance Devices / AITX
Canada Canada
Yvan Rodrigues has 30 years of experience in information systems and software development for the industry. He is Senior Concept Designer at Robotic Assistance Devices

He is a Certified Technician (C.Tech.), a professional designation granted by the Institute of Engineering Technology of Ontario (IETO).

Yvan draws on experience as owner of Red Cell Innovation Inc., Mabel's Labels Inc. as Manager of Systems and Development, the University of Waterloo as Information Systems Manager, and OTTO Motors as Senior Systems Engineer and Senior Concept Designer.

Yvan is currently focused on design of embedded systems.

Comments and Discussions

GeneralRe: Yes, but it would be algorithmically better. You're essentia... Pin
Henry.Ayoola13-Oct-11 1:12
Henry.Ayoola13-Oct-11 1:12 
GeneralRe: The OP's code is O(n^2) unless List has some really sophisti... Pin
Henry.Ayoola13-Oct-11 1:11
Henry.Ayoola13-Oct-11 1:11 
GeneralRe: Good points! The problem that both solutions face is that b... Pin
Yvan Rodrigues11-Oct-11 5:21
professionalYvan Rodrigues11-Oct-11 5:21 
GeneralReason for my vote of 4 Simple idea but efficacious! Pin
SandroBoz10-Oct-11 22:43
SandroBoz10-Oct-11 22:43 
General Pin
Henry.Ayoola10-Oct-11 4:03
Henry.Ayoola10-Oct-11 4:03 
GeneralRe: I did exactly what the OP did before I discovered the Fisher... Pin
Wjousts11-Oct-11 4:38
Wjousts11-Oct-11 4:38 

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