Save and Load .mat files with different names that numerically go up automatically. Maybe in a for loop?

How do I automatically name and save files at iteration of a for loop with the names of the files being attached to the file name to be saved? e.g. first run nameoffile_1, second run nameoffile_2 etc?

And then be able to load them later, also automatically for a set of the runs I've done in the for loop? E.g. if I wanted to load the files from runs 1-10, or 5-20?

At the moment, I'm saving the file as such:

for j=1:n
    fvalagg=j^2 %as an example
    save(['c://Outputs/Scenario' num2str(j) '_fvalagg.mat'],'fvalagg')
end

This seems to correctly save each fvalagg as "Scenario_1fvalagg", then "Scenario_2fvalagg" etc.

But then when I load them, the name of the file loaded is still "fvalagg", rather than "Scenario_1fvalagg".

That's not a problem, as long as there is a way to load multiple of these in one go, without them all overwriting each other as fvalagg.

As I will want to analyse the data for e.g. scenarios 1-10, so I would like to be able to load all the fvalagg generated from loop of j=1:10, and have them loaded up in separate files e.g. fvalagg1, fvalagg2 etc open at the same time.

Thanks!

Answer 1

[Stephen23]

"...as long as there is a way to load multiple of these in one go, without them all overwriting each other as fvalagg"

This is trivial using indexing into an array... and this is the recommended approach.

Simply load into an output argument (which is a scalar structure), obtain the data from whichever fields you want, and then use indexing to allocate that data to a cell array (or a structure, a table, a numeric array, etc.). For example:

D = 'c://Outputs';
V = 5:20;
N = numel(V);
C = cell(1,N); % preallocate
for k = 1:N
    F = sprintf('Scenario%d_fvalagg.mat',V(k));
    C{k} = load(fullfile(D,F)); % allocate using indexing
end
S = [C{:}] % optional

All of the files' data will be in the non-scalar structure S:

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

".I would like... have them loaded up in separate files e.g. fvalagg1, fvalagg2 etc"

Putting numbers into variable names is a sign that you are doing something wrong. Do NOT do this unless you want to force yoiurself into writing slow, complex, buggy code that is hard to debug:

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

[In-chan Kim]

Thanks very much Stephen!

Is it possible to load into one matrix with each of the outputs adding on sequentially?

And thanks for letting me know about the naming; message taken!

[Stephen23]

"Is it possible to load into one matrix with each of the outputs adding on sequentially?"

Yes, it is certainly possible to add the imported numeric matrices into an existing numeric array. For this to work efficiently you need to know the size of the matrices beforehand (otherwise it is simplest to put them into a cell array or structure array inside the loop and concatenate them together afterwards, similar to my original answer).

rows = number of rows in each matrix
cols = number of columns in each matrix
D = 'c://Outputs';
V = 5:20;
N = numel(V);
A = nan(rows,cols,N); % preallocate numeric array
for k = 1:N
    F = sprintf('Scenario%d_fvalagg.mat',V(k));
    S = load(fullfile(D,F));
    A(:,:,k) = S.fvalagg; % allocate using indexing
end

See also:

https://www.mathworks.com/help/matlab/math/multidimensional-arrays.html

https://www.mathworks.com/help/matlab/math/array-indexing.html

[In-chan Kim]

That's really helpful, thanks Stephen!