How to save function variable to file in MATLAB

Question

I want to make a script that saves multiple base variables from the "base name". My attempt looks like this :

function [outargs] = save_with_basename(b)

basePath = 'C:\path\';

Var1 = evalin('base', [b '_1']);
Var2 = evalin('base', [b '_2']); % .. etc

for i=1:N
    save([basePath b '_' int2str(i) '.mat'], ['Var' int2str(i)]);
end

end

This saves the files but the variable saved in the file is called Var1 (see the pic.), but I want it to be called 'Foo_1' if the function was called with :

save_with_basename('Foo');

I think the second argument to save works with the function variable, so it looks like I have to change its name dynamically (which is probably not possible?) , so I wonder if there is a way I can do it.

Here is the problem :

Thanks for any help !

Andras Deak -- Слава Україні · Accepted Answer · 2015-10-12 23:03:12Z

4

For the sake of everything that is holy, please do not do this.

If you really have to, please please please do not do this.

If you really really really ~~have to~~ want to, you indeed need to use dynamic variables (but that doesn't make much of a difference now, does it?):

for i=1:N %what's N again?
   evalin('base',['Var' num2str(i) '=' b '_' num2str(i)]);
   evalin('base',['save([''' basePath b '_' num2str(i) '.mat''], [''Var' num2str(i) '''])']);
end

This will essentially perform

Var1 = "b"_1; %with whatever b is
Var2 = "b"_2;
...
save(['C:\path\b_1.mat'],['Var1']); %with whatever b is
save(['C:\path\b_2.mat'],['Var2']);

in your base workspace, so it will generate the Var* variables there. Small price to pay for selling your soul to the devil. Note that I may have missed the escaping of the single quotes in the second evalin.

edited Oct 12, 2015 at 23:03

answered Oct 12, 2015 at 22:51

Andras Deak -- Слава Україні

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8 Comments

jeff Over a year ago

Thanks for your answer Andras. Yes this is probably not the best way to do what I'm doing. But I remember I wanted to do this before, too. Just wondered if there is a simple solution. Thanks again.

Andras Deak -- Слава Україні Over a year ago

@halilpazarlama I would suggest avoiding the generation of b_1,b_2,... in the first place: use cells, structs or arrays depending on your data. Then you can pass the whole data set to your function for export. Hint: you can access varname.fieldname like this: fieldstr='fieldname'; varname.(fieldstr).

jeff Over a year ago

Keeping them as fields or cell contents would probably be better, yes. But in my case there are few (N=3) but each one contains big matrices. And I'm working on a PC with a limited memory, (also have to share them with Dropbox) So I want to save them inside separate files, in case I want to use only one of them.

Andras Deak -- Слава Україні Over a year ago

@halilpazarlama, all I'm saying is that instead of b1,b2,b3, have b{1},b{2},b{3}; then you can pass b, the cell, to your exporting function, which can then do Var1=b{1}; Var2=b{2}; Var3=b{3}; save(...,Var1); and so on. Worst case scenario: you need a single eval for the generation of the var name Var1. Or you could use structs, like b.f1, b.f2, b.f3, after which for i=1:N, Var.(['f' num2str(i)])=b.(['f' num2str(i)]); end, and --- tadaa --- no more evals;)

jeff Over a year ago

I think I understand now. Ok I will try like this. Thanks :)

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