Turning numbers into letters based on alphabetical order

Hi all, I am trying to export multiple matrix variable that change in size to an excel file. To get their spacing right I need to give a cell name (eg. 'B3') where I want the variable to be placed. However, I want to be able to space my matrices based on their number of columns, which mean taking a length() command and turning it into a letter. Is there any built in way in matlab to do this. an example of what I'm looking for is below.

function(7)

      ans G  (because it is the 7th letter in the alphabet)

There may be an easier way of doing this with xlswrite but I dont know it. Thanks

Brendan

[Christian Lopez Garcia]

num=26;

position = alphabet(num)

function position=alphabet(num)

mult=floor(num/26);

diff=num-26*mult;

symbols = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';

range=26.*[1:26];

if num>26

for i=1:length(range)

if (num >= range(i) && num <= range(i+1))

start=string(symbols(i))

end

end

if diff > 0

extension=string(symbols(diff))

position=char(start+extension+'1')

else diff=0

extension=string(symbols(26))

position=char(start+extension+'1')

end

else

position=string(symbols(num));

position=char(position + '1');

end

end

Answer 1

[Titus Edelhofer]

Hi Brendan,

something like this:

n = 7;
char('A'+(n-1))

What I forgot: you might also think about taking

n1 = rem(n, 26);
n2 = floor(n/26);

in order to have e.g. "AE" for n=31 ...

Titus

[Brendan]

Thanks this worked great.

[Julian Ehlers]

This problem resembles converting to base 26, except that we want a different set of symbols than dec2base gives, and the handling of zeros is a bit different. Borrowing from the dec2base code, this function converts a number to an excel-style column index for arbitrary n:

function lets = letters(nums)
lets = arrayfun(@(n)num2char(n),nums,'UniformOutput',0);

function s = num2char(d)
  b = 26;
  n = max(1,round(log2(d+1)/log2(b)));
  while (b^n <= d)
    n = n + 1;
  end
  s(n) = rem(d,b);
  while n > 1
    n = n - 1;
    d = floor(d/b);
    s(n) = rem(d,b);
  end
  n = length(s);
  while (n > 1)
    if (s(n) <= 0)
      s(n) = b + s(n);
      s(n-1) = s(n-1) - 1;
    end
    n = n - 1;
  end
  s(s<=0) = [];
  symbols = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
  s = reshape(symbols(s),size(s));
end

end

For example:

letters([1,26,27,52,53,26*26,26*26+1,27*26,27*26+1,34*26+1])

gives:

      'A'    'Z'    'AA'    'AZ'    'BA'    'YZ'    'ZA'    'ZZ'    'AAA'    'AHA'

[Guillaume]

Julian, your answer is probably the most comprehensive so you may consider reposting it as an actual answer rather than a comment, so you can at least get some votes for it, even if it can't be the accepted answer anyway.

That is, if you want some reputation points.

[Titus Edelhofer]

Or you might submit this to the File Exchange, if nothing similar is there already ...

Answer 2

[the cyclist]

There's not an explicit builtin for this, but it is easy to write:

function c = letterRankToLetter(n)

c = char('A'+n-1);

end

This will only work for n in the range 1-26, so you might want to put some error-checking in there.