How can I load .mat files?

Question

MByk 2021-10-14

1
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1563536-how-can-i-load-mat-files

评论： MByk 2021-10-19

Hello, I have 3 .mat files and I want to measure feature importance. Following code works fine with .txt files but I am getting an error message with .mat files. I want to load all .mat files one by one and seperate predictors (X) and response variable (Y, the last column) for "fscchi2" function but I can't. How can I fix it?

matFiles = dir('Datasets/*.mat'); 
nFiles = length(matFiles);        
for i = 1:nFiles
    DataSet = load(matFiles(i).name);
    
    X = DataSet(:,1:end-1);
    Y = DataSet(:,end);
    [~,Scores] = fscchi2(X,Y);    
end

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MByk 2021-10-18

编辑：MByk 2021-10-18

As you mentined .mat files were loaded into a scalar structure and I couldn't find a way to seperate response column like I did with the .txt files. Anyway, this not a good way of programming but I solved the problem like this:

for i = 1:3
    switch i
        case 1
            load('Datasets/a.mat')
            X = a(:,1:end-1);
            Y = a(:,end); 
        case 2
            load('Datasets/b.mat')
            X = b(:,1:end-1);
            Y = b(:,end);
        case 3
            load('Datasets/c.mat')
            X = c(:,1:end-1);
            Y = c(:,end); 
    end
    
    [~,nCols] = size(X);
    [Idx,Scores] = fscchi2(X,Y);
    ...
end

Stephen23 2021-10-18

编辑：Stephen23 2021-10-18

"I couldn't find a way to seperate response column like I did with the .txt files"

The columns are in the structure field, not the structure itself. So you just need to access its field/s. If the fieldnames change (i.e. the data is very badly designed by someone who wants to make your life harder) then you can use dynamic fieldnames:

https://www.mathworks.com/help/matlab/matlab_prog/generate-field-names-from-variables.html

Rik showed this below.

Avoid loading directly into the workspace (as you show) unless you want to include latent bugs in your code.

Much simpler and more robust code would result if the data had been better designed (i.e. the same variable/field name).

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Answer 1

Rik 2021-10-18

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1563536-how-can-i-load-mat-files#answer_810916

Or:

matfilenames={'Datasets/a.mat','Datasets/b.mat','Datasets/c.mat'};
for k = 1:3
    S=load(matfilename{k});
    fields=fieldnames(S);
    data=s.(fields{1});
    
    X = data(:,1:end-1);
    Y = data(:,end);
    
    [~,nCols] = size(X);
    [Idx,Scores] = fscchi2(X,Y);
    ...
end

Next time, try to give the variables in your mat files the same name, so you can load to a struct array.

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Star Strider 2021-10-18

I provided something substantially similar to that, however never received any feedback on what did or didn’t work, why it didn’t work, or anything else. I deleted my answer when it became obvious that my efforts were apparently futile.

MByk 2021-10-19

I am a victim of misunderstanding. We had a communication problem. I am not a native speaker like you but I'm trying to do my best. My problem was reading .mat files sequentially and separating the last column and the rest into two different variables. I shared my code and a .mat file but they were deleted. Anyway seems like I had trouble explaining my problem. Your efforts were not futile and important for me.

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