What's wrong with my preallocation of images?

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Iana Ladygina 2019-12-20

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https://ww2.mathworks.cn/matlabcentral/answers/497616-what-s-wrong-with-my-preallocation-of-images

评论： Walter Roberson 2019-12-30

folders = dir("photos");
folders = string({folders.name});
folders = folders(~startsWith(folders,"."))
% Preallocate the structure crashImages
crashImages(length(folders)) = struct("Name",folders(end),"Images",cell(1));
for k = 1:length(folders)
    photos = dir("photos\" + folders(k));
    photos = string({photos.name});
    photos = photos(~startsWith(photos,'.'));
   
    % preallocate the cell array images
   
    images = cell(length(photos),1);
    for kk = 1:length(photos)
        im = imread("photos\" + folders(k) + "\" + photos(kk));
        images{kk} = im;
    end
    
    crashImages(k).Name = folders(k);
    crashImages(k).Images = images;
    
    clear images
end
crashImages

I get the error that the cell arrays in the Image field do not have the correct sizes. What could be the problem?

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Catalytic 2019-12-20

It is generally more informative to copy/paste your error messages (all of them) than to summarize them in your own words. That way, we can see for example what line of code was to blame.

Stephen23 2019-12-30

编辑：Stephen23 2019-12-30

在 MATLAB Online 中打开

Simpler and more robust than using startsWith:

S = dir("photos");
folders = setdiff({S.name},{'.','..'});

Note that you can easily use the same structure that dir returns:

S = dir('photos');
S(ismember({S.name},{'.','..'})) = [];
for k = 1:numel(S)
    ...
    S(k).image = images;
end

Also you should use fullfile rather than concatenating strings together.

"I get the error that the cell arrays in the Image field do not have the correct sizes. What could be the problem?"

If you don't show us the complete error message then we have to guess what the problem is.

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Answer 1

Matt J 2019-12-20

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https://ww2.mathworks.cn/matlabcentral/answers/497616-what-s-wrong-with-my-preallocation-of-images#answer_407279

编辑：Matt J 2019-12-20

在 MATLAB Online 中打开

Maybe you meant to have,

crashImages(length(folders)) = struct("Name",folders{end},"Images",cell{1});

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Iana Ladygina 2019-12-30

Sorry, may be I don't understand it well, but how is fullfile() function related to the preallocation?

Walter Roberson 2019-12-30

Your file reference is coming out wrong, so dir is returning empty, so length is 0, so images would be an empty cell. You then interpreted that as being the incorrect size.

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