From: Logan Capaldo <logancapaldo@...>
Date: 2006-03-03T07:25:30+09:00
Subject: Re: Indexing system - ruby newbie


On Mar 2, 2006, at 3:43 PM, A LeDonne wrote:

> On 3/1/06, Logan Capaldo <logancapaldo@gmail.com> wrote:
>>
>> On Mar 1, 2006, at 12:43 PM, Adam Shelly wrote:
>>
>>>> OP wanted:
>>>>
>>>>  ...  24   25   26   27    28    29   ...
>>>>  ... 'X', 'Y', 'Z', 'AA', 'AB', 'AC' ...
>>>
>>> Here's one that uses succ to do the dirty work, but doesn't  
>>> complicate
>>> things with inject:
>>> (note that '@'.succ = 'A')
>>>
>>> def letter n
>>>   l='@'
>>>   n.times{l.succ!}
>>>   l.gsub(/@/,'-')
>>> end
>>>
>>> -Adam
>>>
>>
>> And now for the over-engineered approach to balance out the  
>> golfing <g>:
>> % cat indexer.rb
>> class Indexer
>>    def initialize
>>      @index_cache = ('A'..'Z').to_a
>>      @index_cache.unshift('-')
>>    end
>>
>>    def alpha_index(i)
>>      if res = @index_cache[i]
>>        res
>>      else
>>        @index_cache[i] = alpha_index(i - 1).succ
>>      end
>>    end
>>    alias [] alpha_index
>> end
>>
>> if $0  == __FILE__
>>    idx = Indexer.new
>>    puts idx.alpha_index(27)
>>    puts idx.alpha_index(0)
>>    puts idx[26]
>> end
>>
>> % ruby indexer.rb
>> AA
>> -
>> Z
>>
>>
>
> A different approach from others in this thread... no memoization, no
> math in the method (let to_s(base) handle it), and a loop that only
> runs, at most, as many times as the length of the resulting string.
> The idea is, change to base 26, then "uncarry" the ones. Should be
> fast.
>
>
> def letterize(num)
>     b26 = num.to_s(26).tr("0-9a-p","@-Y")
>     while b26.sub!(/.@/) { |s| (s[0]-1).chr + "Z" }
>     end
>     b26.sub!(/^@/, "")
>     b26 << "-" if b26.empty?
>     b26
> end
>

Thank you, I was trying hard to work out a way to use to_s(26) and  
couldn't quit get it to work