How to load multiple .mat files which are having subfile in .mat format using the loop?

How to load multiple .mat files which are having subfile in .mat format using the loop?

[Sarvesh Kale]

You can also import the mat files in directory using the import data option found under Home tab of MATLAB

Answer 1

[Stephen23]

Unfortunately the data in those MAT files is very badly designed, because each MAT file uses a changing prefix on the variable names. Ugh. Much better would be if the variable names were exactly the same in every MAT file, then your code would be simpler, more efficient, and much more robust.

Do NOT use ASSIGNIN() or try to LOAD() all of those variables directly into the workspace: this will just make the rest of your code slow and complex when you try to access those variables.

But with some effort we can work with what you have:

P = '.'; % absolute or relative path to where the files are saved.
S = dir(fullfile(P,'B007*.mat'))

S = 2×1 struct array with fields:
    name
    folder
    date
    bytes
    isdir
    datenum

for k = 1:numel(S)
    F = fullfile(S(k).folder,S(k).name);
    D = load(F) % ugh ugh ugh, that ugly prefix on those poor variable names!
    D = cell2struct(struct2cell(D),regexprep(fieldnames(D),'^\w\d+_?',''),1); % much better.
    S(k).data = D;
end

D = struct with fields:
    X118_DE_time: [122571×1 double]
    X118_FE_time: [122571×1 double]
    X118_BA_time: [122571×1 double]
         X118RPM: 1796

D = struct with fields:
    X119_DE_time: [121410×1 double]
    X119_FE_time: [121410×1 double]
    X119_BA_time: [121410×1 double]
         X119RPM: 1772

D = [S.data] % aaah, now that is the best way to store your imported data!

D = 1×2 struct array with fields:
    DE_time
    FE_time
    BA_time
    RPM

Now you can trivially access your data using indexing and fieldnames. For example, the second file:

S(2).name

ans = 'B007 1.mat'

D(2).DE_time

ans = 121410×1

-0.0721 0.3031 0.0331 -0.2073 0.0970 0.1745 -0.0869 -0.0551 0.1309 0.0044

D(2).RPM

ans = 1772

https://www.mathworks.com/help/matlab/matlab_prog/access-multiple-elements-of-a-nonscalar-struct-array.html

https://www.mathworks.com/matlabcentral/answers/1656435-tutorial-comma-separated-lists-and-how-to-use-them

[Rajeev Kumar]

Thanks for sharing the code, we have to store the subfile from the main .mat file in a seperate .mat file with the name of 'main_file_name_DE.mat.'

[Mathieu NOE]

it's quite a bit unclear to me

seems that for the time being you have posted two data (mat) files .

what do you mean by "main" mat file and subfile ? the two provided files do not seems to have nay hierarchical relationship ... or am I wrong ?

Answer 2

[Sarvesh Kale]

Hi Rajeev Kumar,

As per my understanding you are trying to import a MAT file which has multiple data inside it, you can use the following script

function importfile(fileToRead1)

newData1 = load('-mat', fileToRead1);

% Create new variables in the base workspace from those fields.
vars = fieldnames(newData1);
for i = 1:length(vars)
    assignin('base', vars{i}, newData1.(vars{i}));
end

Save the above code as a file named importfile.m

Now you should place your MAT files in the same location as this importfile.m script, then simply do the following

importfile('B007 1.mat'); % will load everything inside the mat file 
importfile('B007 0.mat'); % same as above 

This will load the data in the MATLAB workspace, I hope this answers your queries, please accept the answer if it does.

Thank you

[Mathieu NOE]

hmm assignin , really ?

assignin and eval functions - MATLAB Answers - MATLAB Central (mathworks.com)

[Stephen23]

@Mathieu NOE: The author of this code also does not deal with the inevitable mess of variables that the OP will then have in their workspace... showing that once again, magical variable names just cause more problems.

Sadly there seems to be no requirement for TMW staff to learn or recommend efficient or robust MATLAB programming. At the bare minimum, some links to the MATLAB documentation would be helpful:

"Assigning to variables in the caller workspace can make code more difficult to understand, give surprising results to the user (unexpected or redefined variables in their workspace), and have a negative performance impact. The best practice is to have the function return the variables as output arguments."

source: https://www.mathworks.com/help/matlab/ref/assignin.html

[Sarvesh Kale]

I appreciate @Stephen23 for recommending good MATLAB practices and a descriptive answer, I will try to follow them. I am also learning and growing my MATLAB knowledge everyday ! thanks to people like you.

Answer 3

[Mathieu NOE]

hello

I suspect you wante to store the data in a cell array (and not a regular numeric array)

so try this :

matData = 1×2 cell array

{1×1 struct} {1×1 struct}

>> matData{:} struct with fields:

X118_DE_time: [122571×1 double]

X118_FE_time: [122571×1 double]

X118_BA_time: [122571×1 double]

X118RPM: 1796

struct with fields:

X119_DE_time: [121410×1 double]

X119_FE_time: [121410×1 double]

X119_BA_time: [121410×1 double]

X119RPM: 1772

myFolder = 'C:\Users\IIR\Documents\Machine data\12K Drive End Bearing Dataset'; % Define your working folder
if ~isdir(myFolder)
  errorMessage = sprintf('Error: The following folder does not exist:\n%s', myFolder);
  uiwait(warndlg(errorMessage));
  return;
end
filePattern = fullfile(myFolder, '*.mat');
matFiles = dir(filePattern);
for k = 1:length(matFiles)
  baseFileName = matFiles(k).name;
  fullFileName = fullfile(myFolder, baseFileName);
  fprintf(1, 'Now reading %s\n', fullFileName);
  matData{k} = load(fullFileName); % <= here my mod
end

Answer 4

[Sai Sumanth Korthiwada]

Hi Rajeev Kumar,

I understand that you wanted to load multiple '.mat' files which are having subfile in '.mat' format using the loop. To achieve this, please prefer using 'cell array' instead of 'struct'. The error is due to inconsistent sizes of the fileds in the stuct 'matData'.

Please refer to the modified code, where 'matData' is defined as 'cell array' and fields are added into the 'cell array'.

myFolder = 'C:\Users\skorthiw\Downloads\test'; % Define your working folder
if ~isdir(myFolder)
    errorMessage = sprintf('Error: The following folder does not exist:\n%s', myFolder);
    uiwait(warndlg(errorMessage));
    return;
end
filePattern = fullfile(myFolder, '*.mat');
matFiles = dir(filePattern);
matData = {}; % cell array
for k = 1:length(matFiles)
    baseFileName = matFiles(k).name;
    fullFileName = fullfile(myFolder, baseFileName);
    fprintf(1, 'Now reading %s\n', fullFileName);
    matData(k) = {load(fullFileName)}; % data added into cell array
end

%% to access the data in the cell array:
matData{1}.X118_BA_time;
matData{2}.X119_FE_time;

Please refer to Cell Array and Accessing Data in Cell Array for more information.

Hope this helps.