From: Robert Klemme <shortcutter@...>
Date: 2007-07-14T20:25:10+09:00
Subject: Re: Base 26

On 13.07.2007 22:37, Stefan Rusterholz wrote:
> Mike Moore wrote:
>> Hey friends!  What is the best way to convert a Numeric to a string 
>> encoded
>> with base 26?  I want the string to contain just alpha characters, not
>> alphanumeric characters.  For now I'm using num.to_s(26).tr('0-9a-p', 
>> 'a-z')
>> and I'm wondering if there is a more concise way.

I think your solution is pretty concise already.  You could however do 
something like this:

class Integer
   C26 = (?a..?z).to_a.freeze

   def to_b26
     x = self
     s = ""
     until x == 0
       m = x % 26
       s << C26[m]
       x = (x - m) / 26
     end
     s == "" ? "0" : s.reverse!
   end
end

Or, a more generic solution:

class Integer
   def to_base(chars)
     raise ArgumentError if chars.empty?
     return chars[0].chr if self == 0
     x = self
     s = ""
     until x == 0
       m = x % chars.size
       s << chars[m]
       x = (x - m) / chars.size
     end
     s.reverse!
   end
end

Now you can do

irb(main):065:0> 1.to_base( (?a..?z).to_a )
=> "b"
irb(main):066:0> 26.to_base( (?a..?z).to_a )
=> "ba"

And you can even use a String as argument - duck typing at its best!

irb(main):067:0> 7.to_base "01"
=> "111"
irb(main):068:0> 6.to_base "01"
=> "110"

Kind regards

	robert