Ruby monkeypatch: Integer#position_suffix

integer_position_suffix.rb

# 1.position_suffix => "st"
# 2.position_suffix => "nd"
# 3.position_suffix => "rd"
# 4.position_suffix => "th"
# 11.position_suffix => "th"
# 21.position_suffix => "st"
# 345678.position_suffix => "th"

class Integer
  def position_suffix
    if (11..13).include? (self % 100)
      "th"
    else
      case to_s[-1]
      when "1" then "st"
      when "2" then "nd"
      when "3" then "rd"
      else "th"
      end
    end
  end
end