How can I use 'strcat' and 'for loop' to read my Excel data?

Hello, my Excel data name is "b1,b2...b40", and i want to write a code with for loop to read Excel.

for example：

b1 = xlsread('b1.csv'); %read my Excel data [2048*2]

r1 = [b1(:,2)./cal(:,2)]; %calculate my data

b1(:,2) = r1; %cover my original data

%%%%%%%%%%%%%%%%%%%%%%%%%%

I want to use "for loop" to run all my data (40), but it didn't work.

this is my code：

for i=1:40

strcat('b',num2str(i)) = xlsread(strcat('b',num2str(i),'.csv'));

strcat('r',num2str(i))= [strcat('b',num2str(i),'(:,2)') ./ cal(:,2)];

strcat('b',num2str(i),'(:,2)') =strcat('r',num2str(i));

end

Matlab usually said"Subscripted assignment dimension mismatch.", but I don't know how to fix it.

Plz help me, or recommend me, thank you everyone.

[Stephen23]

Do NOT dynamically name variables! Dynamically naming variables is one way that beginners force themselves into writing slow, complex, buggy code that is hard to debug. Read this to know why:

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

Much simpler and more efficient is to use indexing, exactly as the MATLAB documentation shows:

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

Please upload a sample data file by clicking the paperclip button.

Answer 1

[KL]

There are better ways to handle multiple files in MATLAB. But the main problem in your attempt is that you're not only trying to create file names to use inside xlsread but you're also trying to create dynamic variables (on the LHS of your xlsread line). That's really bad.

Here are some tips. Use dir to get the list of files on your current folder and you can use this in your for loop. For example,

 %execute line by line and see what you get in the workspace
 folderInfo = dir('*.csv');  %get the file names and stuff
 fileNames = {folderInfo.name}; %extract the file names

 for fCount = 1:numel(fileNames)
    temp_b = xlsread(fileNames{fCount});
    %do your stuff -->r1 = [b1(:,2)./cal(:,2)]; and here b1 is temp_b
    ...
 end

you don't need dynamic variables. If you want to write the new data into the file, use xlswrite or csvwrite.

Goodluck!

Links:

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

https://www.mathworks.com/help/matlab/ref/dir.html

[Stephen23]

And possibly this too:

https://www.mathworks.com/matlabcentral/fileexchange/47434-natural-order-filename-sort

[Wei-Chien Hu]

Thank you for solving my problem.