Structures

Question

Charles 2011-8-13

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/13655-structures

I have loaded data that contain structures. The structures are of the form I have variable : struct1, struct2, struct3.... I have a 'file' with the list of these variables and want to manipulate the data contained in the structures with a for-loop.

Here is what I did:

      for i = 1:numel(files)
           data = files(i).data or data{1}.data
      some code;
end

I have errors like : Improper index matrix reference and other errors, Cell contents reference from a non-cell array object.

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Oleg Komarov 2011-8-13

Please rephrase ("I want to analyse each of the file by giving a text file containing the name of the structures that I want to analyse") and be more clear, maybe with an example of what you have and waht you'd like to achieve: http://www.mathworks.com/matlabcentral/answers/6200-tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer

Charles 2011-8-13

Thanks, I understand the question is poorly phrased and would make some corrections

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Answer 1

Oleg Komarov 2011-8-13

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You could have the following structure:

s.myfield = 10;
s.another = 20;
s.hello   = 30;

Now suppose you have a list with the fieldnames which also happens to be the function to retrieve them from a structure:

fnames = {'myfield','another','hello'};

(Note that I didn't call the list with the name of the function)

Now you can manipulate the structure using dynamic fieldname indexing:

for n = 1:numel(fnames)
    tmp = s.(fnames{n});
    % do stuff with tmp or directly with s.(fnames{n}) 
end

This is a complete reference to manipulate structures: structures

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Jan 2011-8-14

@Charles: Please do not tell us, that "it doesn't work", but post a copy of the error message. Otherwise we waste too much time with guessing.

If fnames contains file names, load the files at first:

data = load(fnames{i}), disp(data.hello)

Oleg Komarov 2011-8-14

How are the variables s and t being created or how are they stored?

If they're stored all in a .mat file then you could:

data = load(myfile.mat)

then

for...

data.(s{n})...

end

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Answer 2

Jan 2011-8-13

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https://ww2.mathworks.cn/matlabcentral/answers/13655-structures#answer_18647

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I'm not sure if this matchs your question, but similar question appear very often here:

If you use LOAD without catching the output to a variable, the output is directly written to the current workspace. Accessing these variables is probe to errors and often causes troubles, e.g. if a locally used variable is overwritten.

Therefore it is much safer and easier to use LOAD with catching the output:

data = load('File.mat');
field = fieldnames(data);
fprintf('  %s\n', field{:});
disp(data.field{1});

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Charles 2011-8-13

I guess I posed my question poorly.

I have variable : struct1, struct2, struct3....

I have a 'file' with the list of these variables and want to manipulate the data contained in the structures with a for-loop.

Here is what I did:

for i = 1:numel(files)

data = files(i).data or data{1}.data

some code;

end

I have errors like : Improper index matrix reference and other error.

Jan 2011-8-13

"I have variable" and "I have a 'file'" is not clear. What is the type andthe contents of "files"? Please post the code completely by editing the original question - *not* as comment or answer. And append a complete copy of the error message, because "and other error" is not exact enough to give an advice.

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