How to load selected columns in a for loop?

Question

Joe 2024-4-15

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https://ww2.mathworks.cn/matlabcentral/answers/2106881-how-to-load-selected-columns-in-a-for-loop

编辑： Shivani 2024-4-17

I am trying to load a lot of data. I wrote a for loop to load the .mat files, but I only want certain columns from the files. The columns I need to load do not change between the data sets.

For example, how do I load columns 2, 5, 200, etc inside the loop?

for i= [1:5 7:156]
    for ii = [6 157:244]
        load(['LL_00' num2str(i) '.mat'])
            load(['LL_0' num2str(ii) '.mat'])
    end
end

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Mathieu NOE 2024-4-15

在 MATLAB Online 中打开

simply load all the data then select which cols you want

col_selected = [2;5;200];
data_selected = data(:,col_selected);

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Answer 1

Shivani 2024-4-17

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https://ww2.mathworks.cn/matlabcentral/answers/2106881-how-to-load-selected-columns-in-a-for-loop#answer_1442771

编辑：Shivani 2024-4-17

在 MATLAB Online 中打开

Hello @Joe,

Please note that in MATLAB .MAT files can contain multiple variables of various sizes, so loading specific columns would require knowing the variable names inside those .MAT files.

To load specific columns from variables within .MAT files, you would first load the file and then extract the columns you need from the loaded variables. I assuming that the variable from which you are looking to extract columns to be 'data’ in the code snippet below.

columns_to_extract = [2, 5, 200]; 
for i = [1:5, 7:156] 
    loaded_data_i = load(filename_i); 
    specific_columns_i = loaded_data_i.data(:, columns_to_extract);  
end 

I hope this helps!