fieldnames not order as expected

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Yu Li 2019-5-6

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/460600-fieldnames-not-order-as-expected

编辑： Adam Danz 2019-5-8

Hi:

I saved a serious of parameters in order into a matfile, but after I read it, the 'fieldnames' function does not return the field names neither in order of time saved nor in order of parameter names in alphabete.

This is not a big issue and I can fix it by adding some additional rows of command, but still ask here to want know if there is any reason behind this phenomenon. below are the test code:

para1=1:5;
para2=1:5;
para3=1:5;
save('test','para1','-v7.3');
save('test','para2','-append','-nocompression')
save('test','para3','-append','-nocompression')
tmp=matfile('test');
fieldnames(tmp)

Thanks!

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Adam Danz 2019-5-7

编辑：Adam Danz 2019-5-8

Yes, that's what my comment indicates as well. It addressed your original inquiry,

"the 'fieldnames' function does not return the field names neither in order of time saved nor in order of parameter names in alphabete."

Walter Roberson 2019-5-7

在 MATLAB Online 中打开

sort(properties(tmp))

There was never any promise that properties (or fields) would be in a particular order when requested.

I chased through the code again, and I was able to prove that the properties are added in the order you would expect. However, the built-in addprop@dynamicprops https://www.mathworks.com/help/matlab/ref/dynamicprops-class.html does something that results in the properties not being reported back in the expected order.

The exact order that properties appear in is not consistent, just consistent in small runs. I speculate that it ends up doing something like sorting by internal address of the struct it creates.

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