Storing a vector in a loop each time with a different name

for k = 1:10

    FileName1 = ['EqvStr_',num2str(k),'.csv'];

    filename1 =fullfile('E:\ANSYS_FILES\BigKB', FileName1);

    A = xlsread(filename1,'A2:E1000');

    vectorname = ['a',num2str(k)];
    vectorname = A(:,1);           
end
    disp(a1)
    disp(a2)
    disp(a3)
    disp(a4)
    disp(a5)
    disp(a6)
    disp(a7)
    disp(a8)
    disp(a9)
    disp(a10)

So I am running the above code and MATLAB gives me an error message saying "Undefined function or variable 'a8'". It is weird because it IS showing me the results if I comment out the a8, a9, and a10 lines from the code but gives me the error message if not. There are a 1090 files in the folder in that name format and I am just testing the code with the first 10 but it is showing me this error. Can anyone please help me understand what the problem here is?

[Stephen23]

"Can anyone please help me understand what the problem here is?"

Bad code design. Much better code design would simply use simpler, more efficient indexing with a cell array, exactly as the MATLAB documentation shows:

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

What you are doing will force you into writing slow, buggy, complex code which is harder to debug:

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

[Siddhant Chandra]

Thanks Stephen! I will improve it.

Answer 1

[James Tursa]

This is not the best way to do this in MATLAB. There are many, many posts on this site explaining why. Instead, you should use cell arrays. E.g.,

A{k} = xlsread(filename1,'A2:E1000');

Then downstream in your code simply use A{k} instead of the a1, a2, etc that you are currently using. See this link:

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

[Siddhant Chandra]

Thanks a lot, James! I will read through the links and improve it.

[Siddhant Chandra]

for k=1:10
    FileName1 = ['EqvStr_',num2str(k),'.csv'];
    filename1=fullfile('E:\ANSYS_FILES\BigKB', FileName1);
    A{k} = xlsread(filename1,'A2:E1000');
   end
    disp(A{k})

Hi James, this shows me this error: "Cell contents assignment to a non-cell array object." What I need to perform is to read the first column (2nd row to last row) for all the 1000+ files and store them in different vectors named according to those file names. For eg; A1 corresponding to file EqvStr_1, A2 to EqvStr_2 etc.

[Siddhant Chandra]

James, doesn't A{k} create a k-by-k cell array?

[Siddhant Chandra]

Oh it works now! I put a clear all at the beginning.

[Stephen23]

@Siddhant Chandra: try it and find out: assuming that C does not exist, try this:

C{4} = 1

What does it create?

But your question is actually a good one, because to make the code clear, efficient, and to prevent interference from existing variables you should preallocate the cell array before the loop, like this:

N = 10;
C = cell(1,N); % preallocate!
for k = 1:N
    ...
    C{k} = xlsread(...);
end

Then it is unambiguous what size C has, and what the indexing refers to. Note that the MATLAB documentation clearly shows the cell array being preallocated before the loop:

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

You can read about array preallocation here:

https://www.mathworks.com/help/matlab/matlab_prog/preallocating-arrays.html

https://www.mathworks.com/help/matlab/matlab_prog/preallocate-memory-for-a-cell-array.html

Using clear is not recommended for this, it is better to preallocate.

[Siddhant Chandra]

Got it! Thank you so much for your help Stephen! Thank you for the knowledge