Unzipping MDF4 files and combining them into 1

I am trying unzip a collection of mdf4 files, combine them into 1 mdf4 file and save it. I am getting the following error (attached):

'Time_10Hz' does exist in the dataset as shown (attached)

Any help would be appreciated! Code is attached below

% Open file selection dialog to choose MDF files

[fileNames, folderPath] = uigetfile('*.mdf;*.zip', 'Select MDF or ZIP files', 'MultiSelect', 'on');

if ~ischar(fileNames) % Check if any file is selected

combinedData = struct(); % Initialize an empty structure to store combined data

for i = 1:numel(fileNames)

filePath = fullfile(folderPath, fileNames{i});

% Check if the file is a ZIP archive

if endsWith(filePath, '.zip')

% Unzip the archive to a temporary folder

tempFolder = tempname;

unzip(filePath, tempFolder);

% Find the MDF file(s) in the temporary folder

mdfFiles = dir(fullfile(tempFolder, '*.mdf'));

for j = 1:numel(mdfFiles)

mdfFilePath = fullfile(tempFolder, mdfFiles(j).name);

data = mdfimport(mdfFilePath);

% Extract desired channel groups and signals

desiredChannelGroups = {'32'}; % Replace with your desired channel groups

desiredSignals = {'YawRate', 'EPBMode'}; % Replace with your desired signals

for k = 1:numel(desiredChannelGroups)

channelGroup = desiredChannelGroups{k};

if isfield(data, channelGroup)

for l = 1:numel(desiredSignals)

signal = desiredSignals{l};

if isfield(data.(channelGroup), signal)

if isfield(combinedData, [channelGroup '.' signal])

combinedData.([channelGroup '.' signal]) = [combinedData.([channelGroup '.' signal]), data.(channelGroup).(signal)];

else

combinedData.([channelGroup '.' signal]) = data.(channelGroup).(signal);

end

end

end

end

end

end

% Clean up the temporary folder

rmdir(tempFolder, 's');

else

% Import the MDF file directly

data = mdfimport(filePath);

% Extract desired channel groups and signals

desiredChannelGroups = {'32'}; % Replace with your desired channel groups

desiredSignals = {'YawRate', 'EPBMode'}; % Replace with your desired signals

for k = 1:numel(desiredChannelGroups)

channelGroup = desiredChannelGroups{k};

if isfield(data, channelGroup)

for l = 1:numel(desiredSignals)

signal = desiredSignals{l};

if isfield(data.(channelGroup), signal)

if isfield(combinedData, [channelGroup '.' signal])

combinedData.([channelGroup '.' signal]) = [combinedData.([channelGroup '.' signal]), data.(channelGroup).(signal)];

else

combinedData.([channelGroup '.' signal]) = data.(channelGroup).(signal);

end

end

end

end

end

end

end

% Create a timetable from the combined data structure

timeField = 'Time_10Hz'; % Assuming 'Time' is the field containing time information

combinedTimetable = timetable(combinedData.(timeField), combinedData);

% Save the combined data to a new MDF file

[fileName, folderPath] = uiputfile('*.mdf', 'Save Combined MDF File');

if fileName ~= 0 % Check if a file name is provided

outputFilePath = fullfile(folderPath, fileName);

mdfWrite(outputFilePath, combinedTimetable);

msgbox('MDF files combined successfully!', 'Success');

end

end

Answer 1

[Samay Sagar]

In my understanding., the problem lies in the handling of the time field and combining the MDF files. Instead, you can use the “mdfRead” function to read MDF files as timetables and then append these timetables and store the resultant table as MDF file using “mdfWrite”. In this case, you will not need to manually specify the time fields as the entire tables will be concatenated.

Here is a revised approach to your task:

[fileNames, folderPath] = uigetfile('*.mf4;*.zip', 'Select MDF or ZIP files', 'MultiSelect', 'on');

if ~ischar(fileNames) && ~isempty(fileNames) % Check if any file is selected
    combinedTimetable = timetable(); % Initialize an empty timetable to store combined data
    
    for i = 1:numel(fileNames)
        filePath = fullfile(folderPath, fileNames{i});
        
        % Check if the file is a ZIP archive
        if endsWith(filePath, '.zip')
            % Unzip the archive to a temporary folder
            tempFolder = tempname;
            unzip(filePath, tempFolder);
            
            % Find the MDF file(s) in the temporary folder
            mdfFiles = dir(fullfile(tempFolder, '*.mf4'));
            
            for j = 1:numel(mdfFiles)
                mdfFilePath = fullfile(tempFolder, mdfFiles(j).name);
                
                tt = mdfRead(mdfFilePath);
                
                % Append the data
                if size(combinedTimetable, 1) == 0
                combinedTimetable = tt{:};
            else
                combinedTimetable = [combinedTimetable; tt{:}];
            end
            end           
            % Clean up the temporary folder
            rmdir(tempFolder, 's');
        else
            % Import the MDF file directly as a timetable
            tt = mdfRead(filePath);           
            % Append the data
            if size(combinedTimetable, 1) == 0
                combinedTimetable = tt{:};
            else
                combinedTimetable = [combinedTimetable; tt{:}];
            end
        end
    end
    combinedTimetable = sortrows(combinedTimetable);
    % Save the combined data to a new MDF file
    [fileName, folderPath] = uiputfile('*.mf4', 'Save Combined MDF File');
    if fileName ~= 0 % Check if a file name is provided
        outputFilePath = fullfile(folderPath, fileName);
        mdfWrite(outputFilePath, combinedTimetable);
        msgbox('MDF files combined successfully!', 'Success');
    end
end

For more information about “mdfRead” and “mdfWrite”, you can refer the following documentation:

https://www.mathworks.com/help/releases/R2023a/autoblks/ref/mdfread.html

https://www.mathworks.com/help/releases/R2023a/autoblks/ref/mdfwrite.html

Hope this resolves your query.