How to get a random number in Ruby
Ruby on-RailsRubyRuby on-Rails-3Ruby on-Rails-4RandomRuby on-Rails Problem Overview
How do I generate a random number between 0
and n
?
Ruby on-Rails Solutions
Solution 1 - Ruby on-Rails
Use rand(range)
From Ruby Random Numbers:
> 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.
As Marc-André Lafortune mentions in his answer below (go upvote it), Ruby 1.9.2 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{ 20 + Random.rand(11) }
#=> [26, 26, 22, 20, 30, 26, 23, 23, 25, 22]
Note:
-
Using
Random.new.rand(20..30)
(usingRandom.new
) generally would not be a good idea, as explained in detail (again) by Marc-André Lafortune, in his answer (again). -
But if you don't use
Random.new
, then the class methodrand
only takes amax
value, not aRange
, as banister (energetically) points out in the comment (and as documented in the docs forRandom
). Only the instance method can take aRange
, as illustrated by https://stackoverflow.com/questions/5722881/generate-a-random-number-with-7-digits/5723105#5723105.
This is why the equivalent of Random.new.rand(20..30)
would be 20 + Random.rand(11)
, since Random.rand(int)
returns “a random integer greater than or equal to zero and less than the argument.” 20..30
includes 30, I need to come up with a random number between 0 and 11, excluding 11.
Solution 2 - Ruby on-Rails
While you can use rand(42-10) + 10
to get a random number between 10
and 42
(where 10 is inclusive and 42 exclusive), there's a better way since Ruby 1.9.3, where you are able to call:
rand(10...42) # => 13
Available for all versions of Ruby by requiring my backports
gem.
Ruby 1.9.2 also introduced the Random
class so you can create your own random number generator objects and has a nice API:
r = Random.new
r.rand(10...42) # => 22
r.bytes(3) # => "rnd"
The Random
class itself acts as a random generator, so you call directly:
Random.rand(10...42) # => same as rand(10...42)
Notes on Random.new
In most cases, the simplest is to use rand
or Random.rand
. Creating a new random generator each time you want a random number is a really bad idea. If you do this, you will get the random properties of the initial seeding algorithm which are atrocious compared to the properties of the random generator itself.
If you use Random.new
, you should thus call it as rarely as possible, for example once as MyApp::Random = Random.new
and use it everywhere else.
The cases where Random.new
is helpful are the following:
-
you are writing a gem and don't want to interfere with the sequence of
rand
/Random.rand
that the main programs might be relying on -
you want separate reproducible sequences of random numbers (say one per thread)
-
you want to be able to save and resume a reproducible sequence of random numbers (easy as
Random
objects can marshalled)
Solution 3 - Ruby on-Rails
If you're not only seeking for a number but also hex or uuid it's worth mentioning that the SecureRandom
module found its way from ActiveSupport
to the ruby core in 1.9.2+. So without the need for a full blown framework:
require 'securerandom'
p SecureRandom.random_number(100) #=> 15
p SecureRandom.random_number(100) #=> 88
p SecureRandom.random_number #=> 0.596506046187744
p SecureRandom.random_number #=> 0.350621695741409
p SecureRandom.hex #=> "eb693ec8252cd630102fd0d0fb7c3485"
It's documented here: Ruby 1.9.3 - Module: SecureRandom (lib/securerandom.rb)
Solution 4 - Ruby on-Rails
You can generate a random number with the rand
method. The argument passed to the rand
method should be an integer
or a range
, and returns a corresponding random number within the range:
rand(9) # this generates a number between 0 to 8
rand(0 .. 9) # this generates a number between 0 to 9
rand(1 .. 50) # this generates a number between 1 to 50
#rand(m .. n) # m is the start of the number range, n is the end of number range
Solution 5 - Ruby on-Rails
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.
Solution 6 - Ruby on-Rails
What about this?
n = 3
(0..n).to_a.sample
Solution 7 - Ruby on-Rails
Simplest answer to the question:
rand(0..n)
Solution 8 - Ruby on-Rails
You can simply use random_number
.
If a positive integer is given as n, random_number
returns an integer: 0 <= random_number
< n.
Use it like this:
any_number = SecureRandom.random_number(100)
The output will be any number between 0 and 100.
Solution 9 - Ruby on-Rails
rand(6) #=> gives a random number between 0 and 6 inclusively
rand(1..6) #=> gives a random number between 1 and 6 inclusively
Note that the range option is only available in newer(1.9+ I believe) versions of ruby.
Solution 10 - Ruby on-Rails
range = 10..50
rand(range)
or
range.to_a.sample
or
range.to_a.shuffle(this will shuffle whole array and you can pick a random number by first or last or any from this array to pick random one)
Solution 11 - Ruby on-Rails
you can do rand(range)
x = rand(1..5)
Solution 12 - Ruby on-Rails
This link is going to be helpful regarding this;
http://ruby-doc.org/core-1.9.3/Random.html
And some more clarity below over the random numbers in ruby;
Generate an integer from 0 to 10
puts (rand() * 10).to_i
Generate a number from 0 to 10 In a more readable way
puts rand(10)
Generate a number from 10 to 15 Including 15
puts rand(10..15)
Non-Random Random Numbers
Generate the same sequence of numbers every time the program is run
srand(5)
Generate 10 random numbers
puts (0..10).map{rand(0..10)}
Solution 13 - Ruby on-Rails
Easy way to get random number in ruby is,
def random
(1..10).to_a.sample.to_s
end
Solution 14 - Ruby on-Rails
Maybe it help you. I use this in my app
https://github.com/rubyworks/facets
class String
# Create a random String of given length, using given character set
#
# Character set is an Array which can contain Ranges, Arrays, Characters
#
# Examples
#
# String.random
# => "D9DxFIaqR3dr8Ct1AfmFxHxqGsmA4Oz3"
#
# String.random(10)
# => "t8BIna341S"
#
# String.random(10, ['a'..'z'])
# => "nstpvixfri"
#
# String.random(10, ['0'..'9'] )
# => "0982541042"
#
# String.random(10, ['0'..'9','A'..'F'] )
# => "3EBF48AD3D"
#
# BASE64_CHAR_SET = ["A".."Z", "a".."z", "0".."9", '_', '-']
# String.random(10, BASE64_CHAR_SET)
# => "xM_1t3qcNn"
#
# SPECIAL_CHARS = ["!", "@", "#", "$", "%", "^", "&", "*", "(", ")", "-", "_", "=", "+", "|", "/", "?", ".", ",", ";", ":", "~", "`", "[", "]", "{", "}", "<", ">"]
# BASE91_CHAR_SET = ["A".."Z", "a".."z", "0".."9", SPECIAL_CHARS]
# String.random(10, BASE91_CHAR_SET)
# => "S(Z]z,J{v;"
#
# CREDIT: Tilo Sloboda
#
# SEE: https://gist.github.com/tilo/3ee8d94871d30416feba
#
# TODO: Move to random.rb in standard library?
def self.random(len=32, character_set = ["A".."Z", "a".."z", "0".."9"])
chars = character_set.map{|x| x.is_a?(Range) ? x.to_a : x }.flatten
Array.new(len){ chars.sample }.join
end
end
It works fine for me
Solution 15 - Ruby on-Rails
How about this one?
num = Random.new
num.rand(1..n)
Solution 16 - Ruby on-Rails
Don't forget to seed the RNG with srand() first.
Solution 17 - Ruby on-Rails
Try array#shuffle
method for randomization
array = (1..10).to_a
array.shuffle.first