I need to reorder a list in a random way but I want to have the same result on a short period of time ... So I have:
var list = new String[] { "Angie", "David", "Emily", "James" }
var shuffled = list.OrderBy(v => "4a78926c")).ToList();
But I always get the same order ... I could use Guid.NewGuid() but then I would have a different result in a short period of time.
How can I do this?
Just perform a Fisher-Yates shuffle, however the random you pass in seed with a fixed value instead of allowing it to just be based on system ticks.
public static class ExtensionMethods
{
public static void Shuffle<T>(this IList<T> list, Random rng)
{
int n = list.Count;
while (n > 1)
{
n--;
int k = rng.Next(n + 1);
T value = list[k];
list[k] = list[n];
list[n] = value;
}
}
}
then in your code do something similar to
public class Program
{
public static void Main(string[] args)
{
var list = new String[] {"Angie", "David", "Emily", "James"};
var baseSeed = Environment.TickCount;
for (int i = 0; i < 100; i++)
{
Random rnd = new Random(baseSeed + i / 10);
var shuffled = list.ToList(); //This is so we don't mutate the original list with Shuffle
shuffled.Shuffle(rnd);
Console.WriteLine(String.Join(",", shuffled));
Thread.Sleep(100);
}
Console.ReadLine();
}
}
This would make shuffled have the same result 10 times in a row then it would change to a new order and keep that new order for 10 times in a row. Every time you run the program you will get a different result because it will use a new base Environment.TickCount to start it's offset from. If you just use new Random() it actually just does new Random(Environment.TickCount)
Random class will always generate the same sequence with the same seed. So your code can be:
Random rnd = new Random(12345); //a constant seed (time? userid? dayOfWeek? etc)
var shuffled = list.OrderBy(v => rnd.Next()).ToList();
