How can I export fields from a series of .mat struct files into seperate .csv files in a loop while maintaining the field names as the new file names?

I have a bunch of struct files inside a folder. The only files present in the folder are the .mat struct files. Each .mat file is a 1x1 struct with 8 fields, and each field is a M x 5 double (M is constant inside the same struct, varying only between struct files). Both the .mat files and the fields are named according to a code for future reference (for simplicity and confidentiality, lets say the .mat files are named like APA1470fG; APA2470fG; APA3480fG (...) and the fields are named like APA4701hJ; APA4702hJ; APA480kJ (...). I need to export each field as a separate .csv file for analysis, but I wanted to create a loop so that I wouldn't have to export each and every single one manually, as there are simply too many fields in total that need to be exported, but I also need to be careful about the file names. Just to note that the actual names for both the struct and fields are very complex, so I don't see a way to load or save files using a logical naming approach in order to keep the existing names.

So, what I wanted to make was a loop that goes as follows:

• Load each struct from the main folder at a time;
• Create a folder inside the main folder with the same name as the .mat struct file;
• Save each field as a .csv file with the same name as the field and save it on the created folder.

I would deeply appreciate if anyone could help me with my problem.

Answer 1

[Arjun]

Hi @Vítor,

As per my understanding, you want to perform file manipulation involving .mat file. Specifically, you want to read .mat files that contain a 1x1 struct and then export each field of this struct as a separate .csv file. Each .csv file should be placed inside a dedicated folder corresponding to the .mat file from which it originated.

We can follow the following steps for automating this process:

• Set the path to the folder containing .mat files
• Use the “dir” function to list all the .mat files in the folder
• Load the data from each .mat file
• Use the “fieldnames” function to obtain the name of the struct’s fields
• Create new folder named after each .mat file
• Loop through each field in the struct and save it as a .csv file using “writematrix” function.

You can refer to the following code for better understanding:

% Address of the folder contain gthe .mat file
mainFolder = 'path_to_your_folder containing .mat files';

% Get a list of all .mat files in the folder
matFiles = dir(fullfile(mainFolder, '*.mat'));

% Scan each .mat file, extract the struct and fields
for k = 1:length(matFiles)
    % Load the kth .mat file after fetching the name
    matFileName = matFiles(k).name;
    matFilePath = fullfile(mainFolder, matFileName);
    dataStruct = load(matFilePath);
    
    % Extract the name of the fields of the struct
    structFieldNames = fieldnames(dataStruct);
    mainStruct = dataStruct.(structFieldNames{1});
    
    % Create a new folder with the same name as the .mat file
    [~, folderName, ~] = fileparts(matFileName);
    newFolderPath = fullfile(mainFolder, folderName);
    if ~exist(newFolderPath, 'dir')
        mkdir(newFolderPath);
    end
    
    % Get field names from the struct
    fieldNames = fieldnames(mainStruct);
    
    % Loop through each field in the struct
    for fieldIdx = 1:length(fieldNames)
        fieldName = fieldNames{fieldIdx};
        fieldData = mainStruct.(fieldName);
        
        % Create a CSV file for each field
        csvFileName = [fieldName '.csv'];
        csvFilePath = fullfile(newFolderPath, csvFileName);
        
        % Write the field data to a CSV file
        writematrix(fieldData, csvFilePath);

    end
end

Please go through the documentation of “dir”, “fieldnames” and “writematrix” functions for better understanding.

• dir: https://www.mathworks.com/help/releases/R2023a/matlab/ref/dir.html?searchHighlight=dir&s_tid=doc_srchtitle#d124e379628
• fieldnames: https://www.mathworks.com/help/releases/R2023a/matlab/ref/fieldnames.html?searchHighlight=fieldnames&s_tid=doc_srchtitle
• writematrx: https://www.mathworks.com/help/releases/R2023a/matlab/ref/writematrix.html

I hope this will help!