Integr#commalize

commalize.rb

class Integer
  def commalize
    to_s.gsub(/\d(?=.{3}+$)/, '\0,')
  end
end

if defined?(RSpec::Core::Runner)
  describe 'Integer#commalize' do
    [
      [       321,        '321'],
      [      -321,       '-321'],
      [     4_321,      '4,321'],
      [    -4_321,     '-4,321'],
      [   654_321,    '654,321'],
      [  -654_321,   '-654,321'],
      [ 7_654_321,  '7,654,321'],
      [-7_654_321, '-7,654,321'],
    ].each do |(int, string)|
      it "returns #{string.inspect} for #{int}" do
        int.commalize.should == string
      end
    end
  end
end