Mono Getting the same sequence using Random

Question

When I run the following code in Mono (and not in Microsoft's C# apparently) in the monodevelop IDE. I get the same sequence of random numbers every time (00111111110110001001). If I change the range to something else e.g. r.Next(0, 5) then I do get random values. This seems very weird to me .. is this a bug or am I doing something dumb?

NOTE: it seems sometimes these numbers are negated.. e.g. I see 11000000001001110110 occasionally.

using System;

namespace TestRNG
{
    class MainClass
    {
        public static void Main (string[] args)
        {
            Random r = new Random ();
            for (int i = 0; i < 20; i++) {
                Console.Write(r.Next(0, 2));
            }
            Console.WriteLine();
        }
    }
}

This is not the "Calling Next() on instances of Random called too closely together and therefore seeded with the same seed from the system clock problem".

Using the following code:

using System;

namespace TestRNG
{
    class MainClass
    {
        public static void Main (string[] args)
        {
            Random r = new Random (Guid.NewGuid().ToByteArray()[0]);
            for (int i = 0; i < 20; i++) {
                int rn = r.Next ();
                Console.WriteLine(rn + " " + (rn % 2));
            }
            Console.WriteLine();
        }
    }
}

I see that I get different values for rn every time but the sequence of values for rn % 2, which is what I suspect r.Next() is returning, is the same old values I always see. This leads me to believe that the Russian? fellow who posted an answer before and was down-voted to oblivion was correct (he's subsequently removed his answer). See http://eternallyconfuzzled.com/arts/jsw_art_rand.aspx for example.

Based on one of the comments below this may only be a mono implementation thing.

Answer 1

Well, extending on what swistak said(because i used the Guid class too), this is the code i made for your issue, is already tested and it works:

using System;
using System.Linq;

namespace pruebaDeNumerosAleatorios
{
class MainClass
{
    public static int RandomNumber()
    {
        Random x = new Random(Guid.NewGuid().ToByteArray().First());
        return x.Next(0, 20);
    }
    public static void Main(string[] args)
    {
        for (int i = 0; i < 20; i++)
            Console.WriteLine(RandomNumber());
    }

}
}

As it was said before, you don't give the time to the internal clock (which you are using as seed) to change between iterations so, the number generated is the same. What i did here is implement the Guid class which generates a 'unique' number, convert it as an array of bytes and just used the first element of the array as seed. i did this in a method because that guarantees me that everytime the method is called a diferent number is generated by the Guid class, so im using a different seed for the random number.

Answer 2

You can generate "more random" number without much higher impact on performance by using Guid class:

Random r = new Random(Guid.NewGuid().ToByteArray()[0]);

Edit: The problem with getting similar values every time is because Random.Next() is taking value from current system clock, so probably there isn't much difference in time between each compilation to generate varied values. Try running your code in a loop and values should be more varied.