Methods call in random order (C#)

Question

I want to write a C# program that executes several methods A(), B() and C() in random order. How can I do that?

Gjorgji, the GUID idea is terrible. Please at least order by Random - or better still, use the most voted algorithm. Take the hint from those votes - the community is telling you which one is better. — Roman Starkov, Jan 26 '11 at 02:04
a very terrible idea, which is why you won't find anything on google if you look for it http://www.google.com/search?q=orderby+%22Guid.NewGuid%22 — Pauli Østerø, Jan 26 '11 at 02:30
@Pauli, your belief is anything that you find on Google is automatically a good idea? — Eric Lippert, Jan 26 '11 at 03:13
@Pauli, you have some serious nerves arguing your point after receiving 6 downvotes and numerous comments explaining your mistake, including two from Eric Lippert. It is becoming abundantly clear that you are not here to give right answers, nor to learn anything; you are here to bolster your ego. — Timwi, Jan 26 '11 at 13:23
@Timwi then let me ask you this one thing. How would you write a OrderBy statement in Linq, that shuffles the returned set, that is reusable for both a IEnumerable and IQueryable source. An Expression Tree calling a method that returns a number is to no use if it will be translated into ie. ORDER BY 4 in sql. Thats not random. — Pauli Østerø, Jan 26 '11 at 17:23
@Pauli Totally irrelevant. How would you write a OrderBy statement in Linq, that shuffles the returned set, that is reusable for both a IEnumerable and IQueryable source, and behind the IQueryable might be an OData data source? An Expression Tree calling a method that returns a number is to no use if it will be translated into ie. $orderby=guid'b0d8e6a5-b728-45a6-96e6-0f16a20e599f' in the URL. — R. Martinho Fernandes, Jan 26 '11 at 19:40
@Pauli: ① “How would you ...” — Given the response in this thread, I wouldn’t. ② The question didn’t ask about `IQueryable`. ③ I can’t even think of a use-case where you even need that in the middle of a complex query. You can always shuffle any result set in C#. — Timwi, Jan 26 '11 at 22:37

score 15 · Answer 1 · edited May 23 '17 at 12:33

15

Assuming a random number generator declared like this:

public static Random Rnd = new Random();

Let’s define a Shuffle function to bring a list into random order:

/// <summary>
/// Brings the elements of the given list into a random order
/// </summary>
/// <typeparam name="T">Type of elements in the list.</typeparam>
/// <param name="list">List to shuffle.</param>
/// <returns>The list operated on.</returns>
public static IList<T> Shuffle<T>(this IList<T> list)
{
    if (list == null)
        throw new ArgumentNullException("list");
    for (int j = list.Count; j >= 1; j--)
    {
        int item = Rnd.Next(0, j);
        if (item < j - 1)
        {
            var t = list[item];
            list[item] = list[j - 1];
            list[j - 1] = t;
        }
    }
    return list;
}

^{_{This Shuffle implementation courtesy of romkyns!}}

Now simply put the methods in a list, shuffle, then run them:

var list = new List<Action> { A, B, C };
list.Shuffle();
list.ForEach(method => method());

edited May 23 '17 at 12:33

Community

1
1

answered Jan 26 '11 at 01:07

Timwi

65,159
33
165
230

The easiest way to shuffle in Linq is to use *OrderBy(m => Guid.NewGuid())* – Pauli Østerø Jan 26 '11 at 01:12
3

@Pauli: It is always easier to write a program that sometimes outputs garbage than one that works reliably. – Timwi Jan 26 '11 at 02:00
1

Aren't you throwing away the results of the `Shuffle` in your usage example? Shouldn't it be: list.Shuffle().ForEach(method => method()); – jasonh Jan 26 '11 at 02:53
1

@jasonh: That would work too, and it would do the same thing. The method returns the same list you put in; it makes no difference whether you use that return value or the original list reference. They point to the same list, which is now shuffled. – Timwi Jan 26 '11 at 13:28

Methods call in random order (C#)

1 Answers1

Linked