Editing Topic: RCR62 Project: RCR | RCRchive home

RCR 62: Kernel::rand to accept Range

submitted by anonymous on 2002-02-11 08:27:03

This is a legacy RCR. If this is your RCR, please resubmit it using the new format and process.

I would like rand() to be able to take a Range as a parameter:

rand(20..30) #=> random number between 20 and 30.

rand(40...50) #=> random number between 40 and 49.

----
=== Add comments here
<h4 class="commentheader">Another approach (, 2002-02-11 10:33:15)</h4>
<div class="commentbody">Range#rand and Array#rand would also be useful:<br>
<br>
  (45..96).rand<br>
<br>
  [23, 67, 34, 68].rand<br>
<br>
Any thoughts on randomly removing an element from an array vs randomly selecting?<br>
</div>
<h4 class="commentheader">That might work (, 2002-02-11 10:54:58)</h4>
<div class="commentbody"><tt>
class Array<br>
  def rand() at super(size)<br>
  end<br>
end
</tt>
<p>
then to put a random item from a range:
<p>
<tt>
(0..10).to_a.rand
</tt>
<p>
to get a random line from a file:
<p>
<tt>
File.new("foo.txt", "r").read.split.rand
</tt>
</p>
One danger of this is that Range.to_a might return a ridiculous number of elements.</div>
<h4 class="commentheader">Interesting idea (cout, 2002-02-12 12:01:08)</h4>
<div class="commentbody"><p>I'm not convinced that it makes sense to make this an instance method.  Here's an implentation that overrides rand() to work on any container that has size() and each() defined:

<pre>
module Kernel
  orig_rand = method(:rand)
  define_method(:rand) do |x|
    if x.respond_to?(:each) and x.respond_to?(:size) then
      raise ArgumentError, "Invalid container size" if x.size == 0
      n = rand(x.size); j = 0
      for y in x do
        break if j == n
        j += 1
      end
      y # return
    else
      orig_rand.call(x) # return
    end
  end
end

p rand(10)
p rand(2..20)
p rand([100, 200, 300, 400])
p rand({1=>2, 2=>3, 3=>4, 4=>5})
</pre></div>
<h4 class="commentheader">Two paramaters.... (seanoc, 2002-04-22 19:10:37)</h4>
<div class="commentbody"><p><code>Kernel#rand(min = 0, max = 1, int = false)</code></p>

<p>Seems excessive to need a range object to specify a lower and upper bound.  It'd be nice to specify whether or not it should be an int too.  ;~)  More sugar.  :~)</p></div>
<h4 class="commentheader">Re: Interesting idea (, 2003-07-03 21:53:01)</h4>
<div class="commentbody">I really like that.  You could also optimize it so that if an object responds to at, (Array or String), it wouldn't iterate through them all.</div>

Back to RCRchive.

RCR Submission page and RCRchive powered by Ruby, Apache, RuWiki (modified), and RubLog