From: Jacob Fugal <lukfugl@...>
Date: 2005-07-20T00:54:06+09:00
Subject: Re: Regarding rand

On 7/19/05, Ben Stephens <foolfodder@gmail.com> wrote:
> I was reading Learn to Program by Chris Pine yesterday, in one bit it says:
>         ' Note that I used rand(101) to get back numbers from 0  to 100, and
> that rand(1) always gives back 0.'
> 
> I was wondering if rand() could support syntax like:
>    rand(0..100)

An extension I've frequently used is this:

module Enumerable
  def  random
    ary = self.to_a
    ary[rand(ary.length)]
  end
end

This is purposefully naive. It won't work with enumerables that don't
terminate (e.g. a sequence generator), but then again, neither will
several other methods from Enumerable, such as select, reject, etc. It
will work, but is inefficient for large non-array Enumerables such as
the range (0..1_000_000) since it has to convert it to a 1_000_000
member array. However, in the most frequent case of a relatively small
array of range, it can be quite useful:

# random number between 1 and 100
number = (1..100).random

# random letter from A to Z
letter = ('A'..'Z').random

# random primary color
color = [ :red, :green, :blue ].random

The first two are much more efficient if I calculate the random
number, but I think this unification of random selection from an
Enumerable is useful. I might possibly write an optimized version for
Range eventually...

Jacob Fugal