From: Rob Biedenharn <Rob@...>
Date: 2007-11-02T02:27:23+09:00
Subject: Re: Number to alpha letter


On Nov 1, 2007, at 12:24 PM, Parv G. wrote:

> Hi,
>
> Is there an out of box utility to convert a number to an alphabet
> letter, like a to_alpha()?
>
> I'm trying to write the content of an array to a row in excel  
> worksheet.
>
> Thanks,
> Parv

This should get you started.  It doesn't exactly work because it goes  
(with _ meaning a space) 'y', 'z', 'a_', 'aa', 'ab', but it's the  
right kind of idea (although the translation args should probably be  
expanded inline).  The funkiness arises from the right-most position  
acting like base 26, but the other positions acting more like base 27.

class Integer
   def to_column
     self.to_s(27).tr((('0'..'9').to_a + ('a'..'q').to_a).join(''),  
([' ']+('a'..'z').to_a).join(''))
   end
end


You could either ignore the issue if you only had to deal with 26 or  
fewer columns:
  ('a'..'z').to_a[self-1]

or split the value (which when I started to write out the pseudo-ruby  
looked so easy that I fixed my fence-post error and made it work):

class Integer
   def to_column
     return 'a' if zero?
     upper, lower = self.divmod 26
     unless upper.zero?
       column = (upper - 1).to_column
     else
       column = ''
     end
     column << (?a + lower).chr
   end
end

I think I'll have to tuck that away somewhere that I'll be able to  
find it again.

-Rob

Rob Biedenharn		http://agileconsultingllc.com
Rob@AgileConsultingLLC.com