Concatenate arrays of different length inside loop

Question

TL 2022-8-10

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1777160-concatenate-arrays-of-different-length-inside-loop

回答： Bruno Luong 2022-8-10

I'm using a loop over study participants to create an array of all nonzero values in each participant's file and want to then concatenate these arrays into one matrix/table/etc.

The problem is that there are different amounts of nonzero values in each file and therefore I cannot combine the arrays. I found the PADCAT function but don't think I can use it here because it only works on arrays, i.e. I cannot use that in the loop to append each new column to the existing matrix. The only solution I have is to use the function after the loop, but for that I need to save every array which I want to avoid (especially because I don't want to create and name variables dynamically in the loop and I didn't find a better solution). Any tip would be much appreciated!0 - Either on how to concatenate the arrays in the first place or on how to use PADCAT in my case.

https://de.mathworks.com/matlabcentral/fileexchange/22909-padcat

for i = 1:length(image_files)
    header = spm_vol(image_files{i});
    image_data = spm_read_vols(header); % image_data is a 350x400x12 double
    
    vox_count = nonzeros(image_data);   % create array of nonzero values for each participant                   
    vox_count_table(:,i) = vox_count;   % put values into table - one column for each participant
end

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Answer 1

Bruno Luong 2022-8-10

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1777160-concatenate-arrays-of-different-length-inside-loop#answer_1024310

在 MATLAB Online 中打开

What's wrong with cell?

vox_count_cell = cell(1, length(image_files));
for i = 1:length(image_files)
    header = spm_vol(image_files{i});
    image_data = spm_read_vols(header); % image_data is a 350x400x12 double
    
    vox_count = nonzeros(image_data);   % create array of nonzero values for each participant                   
    vox_count_cell{i} = vox_count;  
end