How do I seed a random class to avoid getting duplicate random values?

You should not create a new Random instance in a loop. Try something like.

You should not create a new Random instance in a loop. Try something like: var rnd = new Random(); for(int I = 0; I Next(1, 100)); The sequence of random numbers generated by a single Random instance is supposed to be uniformly distributed. By creating a new Random instance for every random number in quick successions, you are likely to seed them with identical values and have them generate identical random numbers.

Of course, in this case, the generated sequence will be far from uniform distribution. For the sake of completeness, if you really need to reseed a Random, you'll create a new instance of Random with the new seed: rnd = new Random(newSeed).

And what is the impact that it has on the Random Class in Java. Util – harigm Feb 23 '10 at 8:10 @harigm: Normally, a (pseudo-)random number generator is a deterministic algorithm that given an initial number (called seed), generates a sequence of numbers that adequately satisfies statistical randomness tests. Since the algorithm is deterministic, the algorithm will always generate the exact same sequence of numbers if it's initialized with the same seed.

That's why system time (something that changes all the time) is usually used as the seed for random number generators. – Mehrdad Afshari Feb 23 '10 at 21:49.

Generally the best idea is to have a single instance of Random per thread - you don't want to create an instance regularly as you'll end up with repeats as you've seen, and you don't want to reuse instances between threads as Random isn't thread-safe. Here's a little class to help with that: using System; using System. Threading; public static class RandomHelper { private static int seedCounter = new Random().Next(); ThreadStatic private static Random rng; public static Random Instance { get { if (rng == null) { int seed = Interlocked.

Increment(ref seedCounter); rng = new Random(seed); } return rng; } } } You can then safely use RandomHelper. Instance from any thread. Ideally, for testability, you should try to use this relatively rarely - treat randomness as a dependency, and pass the Random reference into methods that need it.

Note that: The rng field has the ThreadStatic attribute applied to it, so it's effectively a different variable for each thread. We initialize seedCounter (once) based on the current time, but then increment it in a thread-safe manner each time we need a new instance for another thread.

Public static Random rand = new Random(); // this happens once, and will be great at preventing duplicates Note, this is not to be used for cryptographic purposes.

2 Note that unlike Java, Random in . NET is not thread-safe. Calling Next without appropriate locking mechanisms on different threads might cause corruption of the internal state of the random number generator.

– Mehrdad Afshari Nov 23 '09 at 20:37 @Mehrdad: Or worse; I've had it throw exceptions. – Jason Nov 23 '09 at 20:52.

In case you can't for some reason use the same Random again and again, try initializing it with something that changes all the time, like the time itself. New Random(new System.DateTime(). Millisecond).Next(); Remember this is bad practice though.

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