How to get a random number in Ruby?

Question

In Ruby, how do you generate a random number between 0 and n? In .NET you can create a Random object, does something like this exist for Ruby?

Answer 1

Well, I figured it out. Apparently there is a builtin (?) function called rand:

rand(n + 1)

If someone answers with a more detailed answer, I'll mark that as the correct answer.

Answer 2

What is wrong with rand(range) ?

If you needed a random integer to simulate a roll of a six-sided die, you'd use: 1 + rand(6). A roll in craps could be simulated with 2 + rand(6) + rand(6).

Finally, if you just need a random float, just call rand with no arguments.

(From first result of google search: Ruby Random Numbers)

---

As Marc-André Lafortune mentions in his answer below (go upvote it), Ruby1.9.2 has its own Random class (that Marc-André himself helped to debug, hence the 1.9.2 target for that feature).

For instance, in this game where you need to guess 10 numbers, you can initialize them with:

10.times.map{ Random.new.rand(20..30) } 
#=> [26, 26, 22, 20, 30, 26, 23, 23, 25, 22]

Answer 3

Don't forget to seed the RNG with srand() first.

Answer 4

Apparently srand is called when the ruby interpreter is started.

Therefore unless you have a specific need to reset the seed - extra calls to srand are unnecessary.

Answer 5

Ruby 1.9.2 introduces the Random class, so while you can still use rand, you can now create your own random number generator object. It can be marshaled, among other things.

r = Random.new(42)
r.rand(0...100) # => 51

Available for all versions of Ruby by requiring my backports gem.