Integer patch: ordinal indicator

Integer_ordinal_indicator.rb

# Gives a string for the suffix of the ordinal number
#   example usage:
#       2.suffix => "nd"
#      11.suffix => "th"
#      21.suffix => "st"
#
#    TODO: Figure out what to do about 101?
# by tlehman: Sun 03/04/2012 
class Integer
  def suffix
    # all the oddball suffixes
    sufxs = {1=>"st", 2=>"nd", 3=>"rd"} 
    lastd = self % 10  # gets the last digit of the number
    # notice that there are three exceptions to this rule, 
    # namely, eleventh, twelfth, and thirteenth. For all other numbers 
    # congruent to 1,2 or 3 (modulo 10), we use the oddball suffixes
    if [11,12,13].include? self    # this must be evaluated first, lest we get 11-st
      suf = "th"
    elsif sufxs.keys.include? lastd
      suf = sufxs[lastd]
    else
      suf = "th"
    end
    return suf
  end

  def ordinal_indicator
    return suffix
  end
end