Allocating 500 matrices into one 3D array with a loop

Question

Zoe 2017-11-19

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https://ww2.mathworks.cn/matlabcentral/answers/368002-allocating-500-matrices-into-one-3d-array-with-a-loop

评论： Zoe 2017-11-20

Hello guys, I have about 500 matrices naming after "yfit" + yr/month/date (such as yfit20000115). I want to save all of them into one 3d array, here is my code:

x = zeros(1455,1464,500);
x(:,:,1) = yfit20000115;
x(:,:,2) = yfit20000131;
x(:,:,3) = yfit20000216;
x(:,:,4) = yfit20000303;
x(:,:,5) = yfit20000319;
x(:,:,6) = yfit20000404;
........................ until x(:,:,500)

Can anybody please tell me how to loop through this? Especially, I do not know how to put the names into the loop. I thought about using EVAL, but eval's instruction on matlab seems very short and simple. Please help, thank you!

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Stephen23 2017-11-20

编辑：Stephen23 2017-11-20

@Zoe: simply load the .mat file into one output variable (which is a structure), then loop over the fields of that structure. See Nicolas Schmit's answer to know how to do this.

Do NOT load 500 individual arrays into your workspace and then try to use eval to access them, unless you want to write slow, buggy, complex, inefficient, hard-to-debug code. Read this to why doing that is a very inefficient way to write code:

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

Zoe 2017-11-20

@Stephen Cobeldick: Thank you so much for telling me this! I read through the link and also sent the link to my professor!

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Answer 1

Nicolas Schmit 2017-11-20

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https://ww2.mathworks.cn/matlabcentral/answers/368002-allocating-500-matrices-into-one-3d-array-with-a-loop#answer_292020

在 MATLAB Online 中打开

Use

S = load('your_mat_file');

To load your data into a structure S, Then loop over the fields of S.

fields = fieldnames(S);
x = zeros(1455,1464,500);
for k=1:500
    x(:, :, k) = S.(f{k});
end

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Jan 2017-11-20

在 MATLAB Online 中打开

Or:

S               = load('your_mat_file');
fields          = fieldnames(S);
[fields, index] = sort(fields);
match           = strncmp(fields, 'yfit', 4);
dataCell        = struct2cell(S);
x               = cat(3, dataCell{index});