Naming new sets of data in for loop and dividing matrixes.

Hi,

My goal is to divide a 42x525 matrix into 21 42x25 matrixes.

I have 21 sets of data which I have uploaded into matlab in a short for loop

        for p = -10:10
           filename = strcat('meanfile',num2str(p),'.txt');
           line{p+11}=dlmread(filename,'\t',0,0) ;    
        end

Each data set contain 25 columns and 42 rows, where there are either 18, 32 or 42 rows that have non zero values.

My first code snip made a 1 by 21 cell array where each cell contained a 42x25 matrix. Now to get these into numbers I did a short

for p = 1:21
A = cell2mat(line);
end

This turned by data into a 42x525 matrix. Now what I really want is to divide these into 21 matrixes in a for loop.

I tried something like

for i = 1:21
    strcat('line',num2str(i)) = A(1:end,(1:25)*i)
end

however this does not seem to work.

It might be confusing that the lines that are loaded are named from line-10 to line10 and in matlab I try to name them from line 1 to 21, but that is just to avoid non positive integers in the {}.

[Adam]

Keep it in a 3d array and index into that. One variable is vastly better than 21 variables that you also have problems referring to every time you want to use them!

[Benjamin Karlsen]

thanks!

[Stephen23]

"Now what I really want is to divide these into 21 matrixes in a for loop."

Do NOT do this. Dynamically accessing variable names is one way that beginners froce themselves into writing slow, complex, obfuscated, buggy code that is hard to ddebug. Read this to know some of the reasons why:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

You can trivially use indexing, e.g. with a cell array or an ND array. Indexing is simple, neat, and very efficient, unlike what you are trying to do.

"My goal is to divide a 42x525 matrix into 21 42x25 matrixes."

You can do this easily with just one mat2cell call.

Answer 1

[Bob Thompson]

Why not just load the data into a third dimension from the beginning?

        for p = -10:10
           filename = strcat('meanfile',num2str(p),'.txt');
           line(:,:,p+11)=dlmread(filename,'\t',0,0) ;    
        end

[Benjamin Karlsen]

Thanks! new idea for me, i think I can work with that!

[Stephen23]

A robust alternative is to load into a cell array (as the MATLAB documentation shows), and then concatenate it together after the loop:

V = -10:10;
N = numel(V);
C = cell(1,N);
for k = 1:N
    F = sprintf('meanfile%d.txt',V(k));
    C{k} = dlmread(F,'\t',0,0);
end
A = cat(3,C{:})

https://www.mathworks.com/help/matlab/import_export/process-a-sequence-of-files.html

[Benjamin Karlsen]

thanks! helpfull