likelihood of dice rolls when you roll four six-sided dice, take the top three

higher_dice_rolls.rb

#encoding: utf-8

# http://news.ycombinator.com/item?id=4086325
# … try to generate a table of how likely it was to get various dice rolls when you rolled 4 6-sided dice and took the top 3.

require 'pp'


def dice_roll(sides)
	rand(sides) + 1
end

def run_trials(num_trials, num_sides, num_dice, num_low_to_remove)
	results = Array.new
	num_trials.times do
		rolls = (1..num_dice).map do
			dice_roll(num_sides)
		end
		higher_rolls = rolls.sort[num_low_to_remove..-1]
		results.push higher_rolls
	end
	results
end

def results_string(results)
	results.map{|result|result.join(" ")}.join("\n")
end

def count_number_occurrences(results)
	counts = Hash.new(0)
	results.each do |result|
		result.each do |number|
			counts[number] += 1
		end
	end
	counts.sort
end

def inspect_count(count)
	count.map do |number_count|
		number = number_count[0]
		count = number_count[1]
		"#{number} × #{count}"
	end.join("\n")
end

num_trials = 1000000
num_sides = 6
num_dice = 4
num_low_to_remove = 1
results = run_trials(num_trials, num_sides, num_dice, num_low_to_remove)

# puts results_string(results)
count = count_number_occurrences(results)
puts inspect_count(count)

sample_output.txt

1 × 149134
2 × 380883
3 × 532604
4 × 617414
5 × 654096
6 × 665869