UNDEFINED VARIABLE ERROR AFTER EXECUTING FOR LOOP IN MATLAB

Question

Aybüke Ceren Duran 2019-4-24

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https://ww2.mathworks.cn/matlabcentral/answers/458168-undefined-variable-error-after-executing-for-loop-in-matlab

评论： Walter Roberson 2019-4-24

for k=1:numel(listOfImages)
      data{k}=imread(fullfile(whereImagesReside, listOfImages(k).name));
      data{k}=im2double(rgb2gray(data{k}));
      [r,c] = size(data{k}); % get number of rows and columns in image
      columnMatrix(:,k)=data(:);
      V{k}=data(:);
end
 
meanIntensities = mean(columnMatrix,2);

But I get the error Undefined function or variable 'columnMatrix'. How can I solve this?

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Answer 1

Walter Roberson 2019-4-24

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You did not initialize columnMatrix, and numel(listOfImages) was 0.

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Answer 2

Aybüke Ceren Duran 2019-4-24

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format compact

%Firstly, I converted all the images in the vector form.

whereImagesReside = 'lfwdataset';

%dir function will return the images in a structure array.

listOfImages= dir(fullfile(whereImagesReside, '*.pgm'));

%0x1 structure array is created

data = cell(size(listOfImages));

%pmg files are stored in column matrix columnMatrix in the end of the loop

%below

for k=1:numel(listOfImages)

data{k}=imread(fullfile(whereImagesReside, listOfImages(k).name));

data{k}=im2double(rgb2gray(data{k}));

[r,c] = size(data{k}); % get number of rows and columns in image

columnMatrix(:,k)=data(:);

V{k}=data(:);

end

But how can I initialize columnMatrix to 0?

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Walter Roberson 2019-4-24

The empty structure array from dir is the more immediate problem. You should try putting the complete path in the variable about where the images reside.

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