How to fix this error ? "attempt to reference field of non-structure array"

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houda mejri 2017-3-29

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https://ww2.mathworks.cn/matlabcentral/answers/332491-how-to-fix-this-error-attempt-to-reference-field-of-non-structure-array

评论： Walter Roberson 2020-2-9

Hello, I had this error by declaring testset and classify as global variables. do you have an idea ? thank you

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Stephen23 2017-3-29

编辑：Stephen23 2017-3-29

Aaah, global variables and buggy code (that is almost impossible to debug).

Where is the variable defined? How many functions can access it? When and how is its value changed?

So many questions, and so few answers. Globals are the least recommended way of passing data between workspaces, and come second on this list of bad code practices:

https://blogs.mathworks.com/videos/2010/03/08/top-10-matlab-code-practices-that-make-me-cry/

Buggy, and all experts avoid using them... why would anyone even want to use them?

https://www.mathworks.com/matlabcentral/answers/51946-systematic-do-not-use-global-don-t-use-eval

https://www.mathworks.com/matlabcentral/answers/14857-where-do-people-learn-bad-programming-habits-i-e-goto-global-and-eval

http://www.mathworks.com/matlabcentral/newsreader/view_thread/20760

https://www.mathworks.com/matlabcentral/newsreader/view_thread/254555

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Answer 1

Jan 2017-3-29

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https://ww2.mathworks.cn/matlabcentral/answers/332491-how-to-fix-this-error-attempt-to-reference-field-of-non-structure-array#answer_260830

编辑：Jan 2017-3-29

Stephen's comment is exhaustive. Let me summarize it:

Obviously the variable testset has not been defined before or not in the required way.
Because it is a global variable, debugging is hard. You cannot directly find the code, which has (over-) written its value the last time.
This is the expected and known problem with global variables. If the variables are provided as inputs, it is trivial to use the debugger to find the source of the last change.

Poor solution: Dig in your code until you find the bad declaration of the global variable.

Good solution: Remove the global variables from your code and use a clean providing of inputs and outputs - or even more secure an object oriented approach.

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Jan 2017-3-29

@houda: Now you can provide the dataset and teh classifier as inputs to myfunctiontominimize, see e.g. http://www.mathworks.com/matlabcentral/answers/1971

houda mejri 2017-3-29