Regarding rand

ruby-talk
1

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)

Here's my go:

def random(value)
  if value.class.method_defined? 'entries'
    entries = value.entries
    entries[rand(entries.length)]
  else
    rand(value)
  end
end

this works with arrays and hashes too.

I'm coming to Ruby via RoR and i'm loving it, I should be writing a
web app and i'm playing with Ruby instead.

Ben

2

Ben Stephens <foolfodder@gmail.com> writes:

I was wondering if rand() could support syntax like:

   rand(0..100)

That's a great idea!

Here's my go:

def random(value)
  if value.class.method_defined? 'entries'
    entries = value.entries
    entries[rand(entries.length)]
  else
    rand(value)
  end
end

this works with arrays and hashes too.

Oh, I don't know about that... I'd do something like this:

def random(range)
   case range
   when Integer
     rand(range)
   when Range
     a, b = [range.begin, range.end].sort
     if a.integer? and b.integer? then
       if range.exclude_end?
       then rand(b - a) + a
       else rand(b - a + 1) + a end
     else
       rand * (b - a) + a
     end
   end
end

I'm coming to Ruby via RoR and i'm loving it, I should be
writing a web app and i'm playing with Ruby instead.

That's the downside of using such a powerful language:
You can never stop playing with it! :slight_smile:

···

--
Daniel Brockman <daniel@brockman.se>

    So really, we all have to ask ourselves:
    Am I waiting for RMS to do this? --TTN.

3

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

···

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)