How do I generate a list of n unique random numbers in Ruby?

Question

This is what I have so far:

myArray.map!{ rand(max) }

Obviously, however, sometimes the numbers in the list are not unique. How can I mak

Answer 1

Ruby 1.9 offers the Array#sample method which returns an element, or elements randomly selected from an Array. The results of #sample won't include the same Array element twice.

(1..999).to_a.sample 5 # => [389, 30, 326, 946, 746]

When compared to the to_a.sort_by approach, the sample method appears to be significantly faster. In a simple scenario I compared sort_by to sample, and got the following results.

require 'benchmark'
range = 0...1000000
how_many = 5

Benchmark.realtime do
  range.to_a.sample(how_many)
end
=> 0.081083

Benchmark.realtime do
  (range).sort_by{rand}[0...how_many]
end
=> 2.907445