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save new field to a structure?!

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Ano
Ano on 12 Jul 2017
Answered: Thomas on 15 Mar 2018
Hello! I have a 'myfile.mat' which contains several structures struct1, struct2,... Now I would like to save a new added field to one of the structures let say struct1 but it is not working when reloading the .mat file the newfield is not there, any suggestions ?! thank you !

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Geoff Hayes
Geoff Hayes on 12 Jul 2017
Ano - are you saving the updated structure? Please show the code that you have written to read the myfile.mat, update the (say) struct1, and then save the data back to file.
Adam
Adam on 12 Jul 2017
You haven't included any code as to how you do it which would make it a lot easier for us to know where you are going wrong.

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Accepted Answer

Steven Lord
Steven Lord on 12 Jul 2017
There are a couple good ways to do this. If your MAT-file has a lot of data stored in it, save using the -append flag. Another approach, particularly if you need to modify more than one of the struct arrays stored in the MAT-file, is to load into a struct and save that struct using the -struct flag.
data = load('myfile.mat');
data.struct1.newfield = 42;
save('myfile.mat', '-struct', 'data')
With this approach you don't need to worry about overwriting a variable in your workspace that happens to have the same name as one of the variables in the MAT-file.

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More Answers (2)

Ano
Ano on 12 Jul 2017
I have been googling for almost one hour but no result, this is the code that I am using to save the new added field but I lose all the other structures in my .mat file any ideas ?! thank you!
load ('myfile.mat','struct1')
struct1.newfiled = myMatrix;
save myfile struct1

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Thomas
Thomas on 15 Mar 2018
Try looking at the function "matfile" in help. Matfiles are treated differently than other files, and you may need to set the 'Writable' property to true (Good Luck!). Example:
m = matfile('myfile.mat','Writable',true);
m.struct1.newfield = newfield;

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