Defining a non-predetermined number of variables inside a loop

Hi,

I have the following code for loading all the files from a given folder:

    function out = prepfold
    in = input('what is the folder name?  ');
    d = dir(in);
    cd(in)
    dindex = find(~[d.isdir]);
    for j = 1:min(1,length(dindex))
        fname = d(dindex(j)).name;
        load(fname)
    %make new variable named Sj, as in S1, S2, S3, S4, S5... and analyze them
    end

How do I perform the commented line? I am only reading .txt files with numerical data, so I get only double type variables. Since I don't know the number of files before hand, I cannot preallocate. I don't want to prepare a single file padded with zeros, and I am not very good with cells, arrays or the likes, so help to prepare single variables would be greatly appreciated. Cheers.

Answer 1

[Walter Roberson]

http://matlab.wikia.com/wiki/FAQ#How_can_I_create_variables_A1.2C_A2.2C....2CA10_in_a_loop.3F

Answer 2

[Image Analyst]

Use S(j) or S{j} instead of S1, S2, S3, etc. Use S(j) if you're setting it to a single number. Use S{j} if you're setting it to a string, a structure, an array, etc. See the FAQ on cells for an explanation of cells.

Doesn't j just go up to min(1,length(dindex))? So why can't you preallocate S?

maxJ = min(1,length(dindex));
S = zeros(1, maxJ); % or
S = cell(1, maxJ);

What do you mean when you say "I don't want to prepare a single file padded with zeros" - why would you be preparing a file??? I don't even see an fopen() or fprintf() in there. What file are you talking about? Some kind of output file? Or just a temporary scratch file that you think you need for some reason?

Why are you doing

in = input('what is the folder name?  ');

??? Why not use uigetdir()? It's easier for your user to pick one than to have to type one in and possibly not know the name or misspell it.

It's better to load a mat file into a structure than to just call it.

storedStructure = load(fname);
myVariable = storedStructure.myVariable; % or whatever. 
lastFolderUsed = storedStructure.lastFolderUsed; % or whatever.

Your function never declared "out" so it will throw an exception. Put this as the first line inside the function

out = [];

Then go ahead and define it however you want to.

Answer 3

[Tom]

Thank you both for the replies. Apparently it's impossible to avoid using a cell, unless I am willing to use eval. Image Analyst, thank you for the other helpful comments as well (I meant a zero-padded (or NaN-padded) variable, not file, which would be the result if I tried to prepare a matrix from vectors of variable length. Again, I hate cells, as I can't work with them intuitively like with matrices).

[Walter Roberson]

for K = 1 : length(d)
  fn = ['data_from_file' str2num(K)];
  mydata.(fn) = load(d.name);
end

No cell, no eval.