MATLAB: Loading data from structure, using variable

MATLABstruct

HI
I have loaded a structure format, and in this format, I want to load the y values
What I want to do is to load these structures, not by typing all of them individually, but using for loop
For example, 
freq=2048;
DOF=3;
Axis={'x','y','z'};
CAxis={'X','Y','Z'};
SUBA = zeros(freq*2+1,DOF,DOF);
for i=1:DOF
    for j=1:DOF
        load(strcat('SUB_A5_A1_',string(Axis(i)),'_',string(Axis(j))));
        var=strcat('FRF_A_5__',string(CAxis{i}),'_A_1__',string(CAxis{j}));
        SUBA(:,i,j)=var.y_values.values(1,:);
    end
end
So for each loading structure, their name is like SUB_A5_A1_x_x or SUB_A5_A1_y_y etc…
For each structure, there is one more structure named like FRF_A_5__X_A_1__X or FRF_A_5__Y_A_1__Y etc… (Let's call them 'insidestructure')
I don't want to make all the lines for them, so I first thought using a variable 'var' for naming these 'insidestructure'. However, this didn't work. How can I treat this?
Thanks a lot

Best Answer

The most important step is to always load into an output variable (which itself is a scalar structure):
S = load(...) % always load into an output structure!
Then you can easily access the fields of that structure:
https://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-structure-array.html
In case there is only one variable in the mat file and you do not know its name (i.e the data are very badly designed but out of your control), then you can use this shortcut:
S = load(...); % S is a scalar structure
C = struct2cell(C);
A = C{1} % A is the loaded data array
If the variable saved in the mat file is itself a structure, then A will be that structure. You can use fieldnames to gets a list of its fields, and access the fields as shown here:
https://www.mathworks.com/help/matlab/matlab_prog/generate-field-names-from-variables.html
I would have fixed your code, but it has too many strange "features" for me to understand how it is supposed to work, e.g. the load line does not change in the loops so always loads the same file, the sprintf seems to be totally superfluous, etc.
In any case, this question is a classic example of why forcing meta-data into variable names or fieldnames is very bad data design, forcing users into writing slow, complex, inefficient code to do very basic tasks (like accessing their data). Much beter data design would save the meta-data in variables, not in variable/field names, which would make processing your data much much much easier. I guess that is a lesson learned the hard way.
Related Question