how to load saved workspace in a custom named variable?

Hello,

this is what i am currently doing:

for i=1:length(A)
[y1,y2] = myfun(x,A)

savefile = ['test_'num2str(A(i)) '_and_' num2str(x) '.mat'] ;
save(savefile)
end

so i am currently saving all the workspace to a custom .mat file. Now i need to load those workspaces but i need to load them into struct variables that have the same name of the .mat file because i have a lot of data to work with. I tried with these:

for i=1:length(A) 
['test_'num2str(A(i)) '_and_' num2str(x)] = load(['test_'num2str(A(i)) '_and_' num2str(x) '.mat']);
end

but it says: "Error: Assigning the function output to this expression is not supported."

how can i fix these problem?

[Stephen23]

"i need to load them into struct variables that have the same name of the .mat file because i have a lot of data to work with."

That would be about the worst approach.

Don't paint yourself into a corner of writing slow, complex, inefficient code just to access your data:

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

[Davide Maglione]

i thought that was the best approach! thank you!

Answer 1

[Stephen23]

The efficient approach is to use indexing (rather than anti-pattern dynamic variable names):

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

It is easy to import the file data into one cell array or one structure, e.g. the same one that dir returns:

D = 'absolute or relative path to the folder where the files are saved';
S = dir(fullfile(D,'*mat'));
for k = 1:numel(S)
    F = fullfile(D,S(k).name);
    S(k).data = load(F);
end

and then you can simply access the data from every file using basic and very efficient indexing, e.g. the third file:

S(3).name
S(3).data

If all of your .mat files contain variables with the same names (which is good data design) then you can also un-nest them by concatenating the data structures them into one non-scalar structure, e.g.:

out = [S.data]
out(3).someVariable
out(3).otherThing

https://www.mathworks.com/help/matlab/matlab_prog/access-multiple-elements-of-a-nonscalar-struct-array.html

[Davide Maglione]

Thank you very much for your help! this is surely the best way.

Just one last thing, how can i save my workspace to a custom path? so when i do

S = dir(fullfile(D,'*mat'));

i can target with D a specific folder?

thank you again!

[Stephen23]

You can also use an absolute/relative filename when saving data, e.g.:

D = 'absolute or relative path to the folder where the files are saved';
F = sprintf('test_%d_and_%d.mat',A(i),x);
save(fullfile(D,F))

[Davide Maglione]

that's great! thank you!

Answer 2

[Ameer Hamza]

Naming variables dynamically is not a good idea: https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval. Just load it in a struct array or a cell array.

Struct array:

for i=1:length(A) 
    s(i) = load(['test_'num2str(A(i)) '_and_' num2str(x) '.mat']);
end

or a cell array

C = cell(length(A),1);
for i=1:length(A) 
    C{i} = load(['test_'num2str(A(i)) '_and_' num2str(x) '.mat']);
end