Ruby by Example

#17 Roman Numerals (roman_numeral.rb)

In the previous script, you learned how to change the representation of a number as a String so that it had commas (or some other desired delimiting character) in appropriate places for easier readability. One of the most traditional ways to represent a number as a String is as a Roman numeral. This script adds a new method to all Integers called to_roman. Let’s see it in action in irb.

$ irb -r roman_numeral.rb
irb(main):001:0> 42.to_roman
=> "XLII"
irb(main):002:0> 1.to_roman
=> "I"
irb(main):003:0> 5.to_roman
=> "V"
irb(main):004:0> digits = (0..9).to_a
=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
irb(main):005:0> digits.map { |d| d.to_roman }
=> ["", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"]

If you remember ...