How to get 2 variables form loading mat fille

Question

Rita 2016-2-5

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https://ww2.mathworks.cn/matlabcentral/answers/266826-how-to-get-2-variables-form-loading-mat-fille

评论： Star Strider 2016-2-5

I want to load lots of mat file like (a1_2.mat......a50_40.mat) and take two variables(c,d) from each mat file and then put variables in a matrix like this.[c1 d1; c2 d2.....]

    for n = 1 : 50
    for k=1:40
    y=load(['a',num2str(n),'_', num2str(k) '.mat']);
    c = y.c;% load first variable
    d=y.d; % load second variable and 
    all(:,1)=c;
    all(:,2)=d;
    end
   end

but I can't get the final matrix correctly.

Thanks in advance for your help.

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Answer 1

Walter Roberson 2016-2-5

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https://ww2.mathworks.cn/matlabcentral/answers/266826-how-to-get-2-variables-form-loading-mat-fille#answer_208724

在 MATLAB Online 中打开

    for n = 1 : 50
      for k = 1:40
        y = load(['a',num2str(n),'_', num2str(k) '.mat']);
        c = y.c;% load first variable
        d = y.d; % load second variable and 
        all_vals(n,k,1) = c;
        all_vals(n,k,2) = d;
    end
   end
   all_vals = reshape(all_vals, [], 2);

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Answer 2

Star Strider 2016-2-5

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https://ww2.mathworks.cn/matlabcentral/answers/266826-how-to-get-2-variables-form-loading-mat-fille#answer_208725

在 MATLAB Online 中打开

Assuming that you cannot pre-allocate your matrix, something like this could work:

all_vars = [];
for n = 1 : 50
    for k=1:40
        y=load(['a',num2str(n),'_', num2str(k) '.mat']);
        c = y.c;% load first variable
        d = y.d; % load second variable and
        all_vars = [all_vars; [c d]];
    end
end

I changed the name of your matrix, because all is a function name you could need later in your code. Naming variables the same as built-in MATLAB functions is called ‘overshadowing’. MATLAB will use the variable instead of the function afterwards, making the function useless until you change the variable name.

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Rita 2016-2-5

Thanks Walter for your prompt response.unfortunetly my results had 30 rows of zero number. Thanks Star strider for your explanation.and the result is perfect.