Randomizing an Array of restaurants

Question

For my Intro to computer science class I have to make an application to select restaurants with various capabilities, I can't figure out how to randomize the array though. Below is my code.

string[] myRestaurants = new string[9];

myRestaurants[0] = "Wendy's";
myRestaurants[1] = "Arby's";
myRestaurants[2] = "Olive Garden";
myRestaurants[3] = "The Pie";
myRestaurants[4] = "The Cheesecake Factory";
myRestaurants[5] = "Beto's";
myRestaurants[6] = "Dillinger's Saloon";
myRestaurants[7] = "Dayz Alpher";
myRestaurants[8] = "Firehouse subs";

var nextArray = myRestaurants.ToList();
Random rng = new Random();  
int n = nextArray.Count;
while (n > 1)
{
    n--;
    int k = rng.Next(n + 1);
    T value = nextArray[k];
    nextArray[k] = nextArray[n];
    nextArray[n] = value;
    //bang
}

You can't just declare a generic variable in a method body, that's not how it works. Can you remove everything that isn't relevant? — Jeroen Vannevel, Dec 20 '13 at 03:19

score 5 · Answer 1 · answered Dec 20 '13 at 03:21

5

You can randomize it with LINQ and the OrderBy method.. coupled with your Random class:

myRestaurants = myRestaurants
                    .OrderBy(x => myRandom.Next(myRestaurants.Length))
                    .ToArray();

answered Dec 20 '13 at 03:21

Simon Whitehead

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+1. This will work pretty well, but the obsessive in me wants to point out the [Fisher-Yates shuffle](https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle) is an efficient way to produce a 'fairly' shuffled list. – TheEvilPenguin Dec 20 '13 at 03:25
Why would you put effort in implementing an algorithm when you can do the same with one line of code. I highly doubt restaurant order is crucial and needs top notch randomizing. – Jeroen Vannevel Dec 20 '13 at 03:27
@JeroenVannevel Given it's a three-line in-place algorithm which runs about as efficiently as possible and provides a better distribution, why not? In this case the LINQ method is probably fine, but it's worth noting the proper way to do it when distribution or performance matters. – TheEvilPenguin Dec 20 '13 at 03:33
@TheEvilPenguin If you're interested, I added an answer with the Fisher-Yates mechanism. :) – Abbas Dec 20 '13 at 11:21

score 1 · Answer 2 · edited Dec 20 '13 at 03:44

1

The example below pics items randomly.

Random rand=new Random();
string[] RandomArray = myRestaurants.OrderBy(r => rand.Next()).ToArray();

edited Dec 20 '13 at 03:44

terrybozzio

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answered Dec 20 '13 at 03:31

Darey

497
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score 0 · Answer 3 · answered Dec 20 '13 at 11:19

Here's a generic implementation using the Fisher-Yates mechanism:

public static class Extensions
{
    public static void Shuffle<T>(this IList<T> list)
    {
        var rnd = new Random();

        for (int i = list.Count - 1; i >= 0; i--)
        {
            var r = rnd.Next(i + 1);
            T value = list[r];
            list[r] = list[i];
            list[i] = value;
        }
    }
}

Usage:

myRestaurants.Shuffle();

Example output:

The Pie
Dillinger's Saloon
Beto's
Olive Garden
The Cheesecake Factory
Dayz Alpher
Firehouse subs
Arby's
Wendy's

Randomizing an Array of restaurants

3 Answers3