sequential_grab.rb

# Ruby translation of: http://kaioa.com/node/53#comment-477

probabilities = [1, 1, 1, 1, 1, 1];
unrandomness = 1;

def cumsum(vector)
  _dup = vector.dup
  1.upto(_dup.length - 1) { |i| _dup[i] += _dup[i-1] }
  _dup
end

puts "roll | probabilities"

6.times do
  # find the cumulative probability, and then divide each member
  # by the sum of the probabilities.
  cumprob = cumsum(probabilities)
  _sum = probabilities.reduce(:+).to_f
  cumprob.map! { |n| n / _sum }
  
  # find the first index greater than the cumulative probability
  _rand = rand
  roll = cumprob.index(cumprob.find { |prob| prob >= _rand })
  
  # add unrandomness...
  probabilities.map! { |n| n + unrandomness }
  probabilities[roll] -= 6*unrandomness
  if (_min = probabilities.min) < 0
    probabilities.map! { |n| n - _min }
  end
  
  # pretty printing for the eyes    
  print "  #{roll + 1}  | "
  probabilities.each { |p| print p.to_s.center(4) }
  puts
end