Error using ==> eval

Hi,

I am writing a code to compare several nested structures. Basically I need to compare all the values in cell (x,1) in every structure to the cell (x,1) in every other structure.

My issue right now is with organizing the output. I need the output to be a structure (output) that contains a structure for each subject (subject1) and I want that structure to be named according to a looping variable, x (representing the subject #) and then within that subject1 structure, I want structures for each of the comparison subjects (subject2), also named according to a looping variable, y.

Here is what I have written so far:

function output=hcp_compare(hcp)

output=zeros(843,1);

%for all subjects in x
for x=1:length(hcp)
    %create subject name
    subject1=eval(['subj' num2str(x)]);
      %insert main subject name
    output(x,1).(subject1)(1,1).name=hcp(x,1).name;
    %then loop through evry subject and compare to x  
    for y=1:length(hcp)
        %loop through evry cell in connMatVect and compare for evry xypair
        subject2=eval(['subj' num2str(y)]);
        for z=1:35778
            output(x,1).(subject1)(2,1).comparisons(x,y).(subject2)(z,1)=(hcp(x,1).connMatVect(z,1)-hcp(y,1).connMatVect(z,1));
        end
    end

end

end

I want (subject1) and (subject2) to be replaced by subjx and subjy. But when I run the code, I get the following error:

??? Error using ==> eval
Undefined function or variable 'subj1'.

Error in ==> hcp_compare at 10
    subject1=eval(['subj' num2str(x)]);

So I believe I'm missing something or not understanding something. Can anyone give some pointers?

[Stephen23]

"I believe I'm missing something or not understanding something. Can anyone give some pointers?"

Don't use eval.

Answer 1

[Stephen23]

https://www.mathworks.com/help/matlab/matlab_prog/string-evaluation.html

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

Answer 2

[dpb]

DON'T DO THIS!!! See <generate-field-names-from-variables> for how to do this instead.