Calculate the probability that two people in a given group will have the same first initial and last name.

name_probability

#!/usr/bin/env ruby
# Get name file from https://www.census.gov/genealogy/www/data/1990surnames/names_files.html

names = File.readlines('dist.male.first.txt')
list = {}
letters = ('A'..'Z')
total_people = 40000
last_name_freq = 0.01006 # Smith

letters.each do |letter|
  list[letter] = []
	names.each do |line|
		if line.match("^#{letter}")
			list[letter] += [line[15...20].to_f]
		end
	end
	frequency = list[letter].inject(:+)

	probabilty = 1.0
	number_of_people = (frequency * total_people / 100 * last_name_freq).to_i
	number_of_people.times do |i|
		probabilty *= (10000.0 - i)/10000.0
	end
	p "#{letter}: #{1 - probabilty}"
end