From: Daniel Carrera <dcarrera@...>
Date: 2003-03-29T15:31:14+09:00
Subject: Re: Weighted random selection -- how would you do this?


Say that you have a hash 'events' whose keys are the events you are 
interested in and the values are the corresponding weights:

e.g.
events = { 
	"event1" => 5, 
	"event2" => 17, 
	"event3" => 6, 
	"event4" => 13
}

Solution:
tot = 0; events.each { |event, weight| tot += weight }
val = rand tot
event = events.each do |event, weight|
	val -= weight; 
	return event if val < 0
end

This should work, I think.

On Sat, Mar 29, 2003 at 03:11:58PM +0900, Hal E. Fulton wrote:
> Here's a little question for you.
> 
> Given: A set of items, each with
> an associated integer representing
> the relative likelihood that each
> item will be selected.
> 
> Write: A method that will select
> a random item.
> 
> I've started this a couple of times,
> but have become convinced I'm making
> it too hard, and someone can probably
> come up with a three-liner.
> 
> Any ideas?
> 
> Cheers,
> Hal
> 
> 

-- 
Daniel Carrera
Graduate Teaching Assistant.  Math Dept.
University of Maryland.  (301) 405-5137
--
distrain: distrain (di-STRAYN) verb tr., intr.
   To seize the property in order to force payment for damages, debt, etc.