Merging contents of multiple MAT files

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Multiplexer 2018-10-25

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https://ww2.mathworks.cn/matlabcentral/answers/425992-merging-contents-of-multiple-mat-files

编辑： Stephen23 2022-1-20

Hello,

I got a collection of MAT files (generated by External Mode data archiving) that have names such as below and their count can go into 1000's: - MyMatFile_0.mat - MyMatFile_1.mat (...) - MyMatFile_2999.mat - MyMatFile_3000.mat

What i want to achieve is to merge all the arrays from inside the MAT files vertically together (like [MyMatFile_0.mat ; MyMatFile_1.mat ... ] and save that new single array to a spearate MAT file or simply leave it in workspace.

So for, example, with the files I'm attaching, each of them contains a 20x2 double array and I want to merge them together to make one MAT file with 60x2 double array.

Also, this batch of files is generated per each experiment i do and for each experiment the total number of MAT files may vary and the amount of elements in array in each MAT file also may vary (but there will be always 2 columns).

Any help is appreciated.

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Answer 1

Stephen23 2018-10-25

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https://ww2.mathworks.cn/matlabcentral/answers/425992-merging-contents-of-multiple-mat-files#answer_343316

编辑：Stephen23 2021-4-18

在 MATLAB Online 中打开

To read the files in the correct order download my FEX submission natsortfiles:

https://www.mathworks.com/matlabcentral/fileexchange/47434-natural-order-filename-sort

Then all you need is this (the input and output files are attached):

D = 'path to the folder where the files are saved'
D = '.';
S = dir(fullfile(D,'TestLog_*.mat'));
S = natsortfiles(S); % alphanumeric sort by filename
for k = 1:numel(S)
    T = load(fullfile(D,S(k).name));
    S(k).data = struct2cell(T);
end
M = vertcat(S.data);
save('TestLog.mat','M')

This will work for any number of .mat files, with a few conditions:

each .mat file contains only one variable.
the output file is in a different folder or does not match the dir filename string (otherwise you could end up accumulating the same data repeatedly).

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Stephen23 2018-10-26

编辑：Stephen23 2018-10-26

在 MATLAB Online 中打开

"... would it be difficult to modify the script to work in suituation where MAT fail contains two variables each ..."

Your life would be much simpler if the variable names in each .mat file were exactly the same, then this task would be trivial: if you can change the code that writes the .mat files, then that is the best option:

C = cell(2,...)
for k = ...
    T = load(...);
    C{1,k} = T.hello;
    C{2,k} = T.world;
end

As it is you have a few options:

load the entire .mat file contents into a structure, use fieldnames, match the fieldnames (e.g. strncmp or strncmpi for your fieldnames) and use the indices to allocate to two cell arrays.
load one variable at-a-time using load's -regexp option, and use the same code as in my answer, once for each cell array.
load the entire .mat file contents into a structure, sort the fields using sortfields, convert to cell using struct2cell, use indexing to assign to two cell arrays.

So the answer to your question is "it is not difficult, but it is fiddly... and can easily be avoided by naming the data better".

Hanah Aemilia Choice 2022-1-20

编辑：Hanah Aemilia Choice 2022-1-20

When I run this script (the first posted solution), I get the error message:

Reference to non-existent field 'data'.

Error in displayscript (line 23)

M = vertcat(S.data);

I'm wondering what the cause of this would be.

Stephen23 2022-1-20

编辑：Stephen23 2022-1-20

@Hanah Aemilia Choice

"I'm wondering what the cause of this would be."

No files match the DIR name pattern so S is sempty, so the loop never iterates, so the data field is not created.

Take a look at numel(S)

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Merging contents of multiple MAT files

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