How to append new structure array element in existing .mat file.

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Abdurrehman 2017-2-1

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https://ww2.mathworks.cn/matlabcentral/answers/322891-how-to-append-new-structure-array-element-in-existing-mat-file

评论： Jan 2017-2-2

I am appending new structure array element in existing .mat file (which contains structures), it saves new element accurately but previous values are replaced with empty elements. as stated below

FileName=fullfile('\\Server Location Address');% Address of existing .mat file 
Device(5)=struct('A',1,'B',2,'C',3);
save(FileName,'Device','-append');

The above code save Device(5) elements accurately but it removes all Devices values before 5.

Please help how to append new value in .mat file while don't changing previous ones.

Thanks

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Stephen23 2017-2-1

编辑：Stephen23 2017-2-1

The badly named '-append' option should really be named the '-replace' option. It does not append data onto existing arrays, as the save documentation clearly states: "adds new variables to an existing file. If a variable already exists in a MAT-file, then save overwrites it."

When beginners start to read the documentation then they start to learn how MATLAB works, and they don't have to guess what MATLAB is doing.

Not only that this is such a common topic that it has hundreds of threads already on this forum. This simple search (you can search Answers at the top of the page) gives more than five hundred results:

https://www.mathworks.com/matlabcentral/answers/?term=save+append

Did you read any of them?

Muhammad Abdurrehman 2017-2-1

Read some of them but couldn't found a way that how to append new structure element in existing .mat file

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Answer 1

Stephen23 2017-2-1

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https://ww2.mathworks.cn/matlabcentral/answers/322891-how-to-append-new-structure-array-element-in-existing-mat-file#answer_252931

编辑：Stephen23 2017-2-1

在 MATLAB Online 中打开

You might find that matfile is the easiest way. There are lots of examples and help in the documentation, but depending on your data something like this should work:

 m = matfile(filename,'Writable',true);
 m.device = [m.device,newdata];

or perhaps

 m = matfile(filename,'Writable',true);
 m.device(end+1) = newdata;

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Muhammad Abdurrehman 2017-2-2

This solved my great trouble, thanks a lot

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Answer 2

Jan 2017-2-1

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/322891-how-to-append-new-structure-array-element-in-existing-mat-file#answer_252932

在 MATLAB Online 中打开

If the MAT file is not written in the -v7.3 version, this can help:

FileName  = fullfile('\\Server Location Address');
FileData  = load(FileName, 'Device');
Device    = FileData.Device;
Device(5) = struct('A',1, 'B',2, 'C',3);
save(FileName, 'Device', '-append');