Read multiple .mat files and process them

Hi,

I wanna read some .mat files with name "sub1_hi.mat" to "sub40_hi.mat" that are 4D matrices and process them.

I did the first step with this code:

for j=1:40
load (['s',num2str(j),'_hi_dDTF.mat'])
end

But, when I wanna try this inner loop I got error for the size and imagesc functions.

for j=1:40
    data = load (['s',num2str(j),'_hi_dDTF.mat'])
    [chan1, chan2, freq, winNumber] = size(data);
    for i=1:winNumber
        fig = imagesc(data(:,:,3,i))
        filename = ['dDTF_s',num2str(j),'_hi_beta',num2str(i),'.jpg']
        saveas(fig, filename)
    end
end

Answer 1

[Stephen23]

"As you said in my case the variable's name changes on each iteration of the outer loop."

With changing variable names you will need some complex, fragile code. For example:

for ii = 1:40
    F = sprintf('s%d_hi_dDTF.mat',ii);
    C = struct2cell(load(F));
    assert(isscalar(C),'Only one variable per file!')
    data = C{1};
    [chan1, chan2, freq, winNumber] = size(data);
    for jj = 1:winNumber
        fig = imagesc(data(:,:,3,jj));
        filename = sprintf('dDTF_s%d_hi_beta%d.jpg',ii,jj);
        saveas(fig, filename)
    end
end

Better data design would keep the variable names exactly the same on every loop iteration. Then you could write simple, robust code to process that file data. For example, if the variable is always named "data":

for ii = 1:40
    F = sprintf('s%d_hi_dDTF.mat',ii);
    S = load(F);
    [chan1, chan2, freq, winNumber] = size(S.data);
    for jj = 1:winNumber
        fig = imagesc(S.data(:,:,3,jj));
        filename = sprintf('dDTF_s%d_hi_beta%d.jpg',ii,jj);
        saveas(fig, filename)
    end
end

Answer 2

[Walter Roberson]

The output of load is always a struct that contains one field for each variable that was loaded. Your second code has the right general approach but you need to account for the loaded variable name as a field of data . That is easy enough if the variable name is always the same, but gets a bit messier if the variable names in the files change.

[Reza]

Thanks, Walter for the answer.

As you said in my case the variable's name changes on each iteration of the outer loop. Can you please give me an example of how this code could work correctly?

[Walter Roberson]

Use dynamic field names. Compute the name of the variable and use

data.(variablename)

If the variable name is not known then use fieldnames(data)