From: Gavin Kistner <gavin.kistner@...>
Date: 2007-06-08T03:10:19+09:00
Subject: Re: Mutually-Recursive Functions

From: bbiker [mailto:renard@nc.rr.com] 
Sent: Thursday, June 07, 2007 12:00 PM

> I am not exactly sure what the OP was trying to do .. except that it
> has to do with Columns in Excel. It does seems to me to be fairly
> complicated. If this off topic, please excuse.

[snip]

> # method to convert from numeric column to alpha col
> # accepts numeric column 1 through 256
> # returns alpha column A through IV
> # returns empty string on invalid input
> def n2a_col(num_col)
> 
> 	# verify that it in the range of 1 to 255
> 	return nil if num_col < 1 || num_col > 256
> 
> 	mostSD = num_col / 26  # SD = Significant Digit
> 	leastSD = num_col % 26
> 
> 	if leastSD == 0
> 		mostSD -= 1
> 		leastSD = 26
> 	end
> 
> 	leastSA = ('A'[0] + leastSD - 1 ).chr
> 	mostSA  = mostSD > 0 ? ('A'[0] + mostSD - 1).chr : ''
> 
>   mostSA + leastSA
> end

Not as efficient, but simpler:

def n2a_col( num_col )
  if (1..255).include?( num_col )
    a = 'A'
    ( num_col-1 ).times{ a = a.succ }
    a
  end
end
    
[ 0, 1, 2, 26, 27, 250, 255, 256 ].each{ |n|
 puts "%3d => %s" % [ n, n2a_col( n ).inspect ]
}

#=>   0 => nil
#=>   1 => "A"
#=>   2 => "B"
#=>  26 => "Z"
#=>  27 => "AA"
#=> 250 => "IP"
#=> 255 => "IU"
#=> 256 => nil