From: Daniel Martin <martin@...>
Date: 2006-07-28T03:45:46+09:00
Subject: Re: rand(-10..10)

Daniel Schierbeck <daniel.schierbeck@gmail.com> writes:

>>> This should work with all enumerables:
>>>
>>>    module Enumerable
>>>      def rand
>>>        entries = entries
>>>        entries.at(Kernel.rand(entries.length))
>>>      end
>>>    end
>>>
>>> I can't seem to get around the `entries = entries' part -- I don't want
>>> to convert the enumerable to an array more than once. Any ideas?

There's also this, which is possibly more memory-efficient (if the
Enumerable in question chews large amounts of memory when being
converted to an array, but not with each), but is almost certainly
much slower, since it calls rand once per element:

module Enumerable
  def rand
    ret, i = nil, 0
    each {|v| ret = v if 0 == Kernel.rand(i += 1)}
    ret
  end
end

Test code for irb:

h=Hash.new(0); 10000.times {h[%w{a b c d e}.rand] += 1}; h