MATLAB: Coder error – Directly accessing field or property of nonscalar struct or object not supported for code generation

matlab codernon-scalar structure

The following line of MATLAB code causes the coder error “Directly accessing field or property of nonscalar struct or object not supported for code

Generation”

healthy = ~Health(SignalIndex).HasData(SatIndex,EphemIndex);

I have seen the following Mathworks page:

https://uk.mathworks.com/matlabcentral/answers/439222-matlab-coder-error-directly-accessing-field-or-property-of-nonscalar-struct-or-object-not-supported

The work around cited doesn’t address my particular problem (or I can’t see that it does). Can you suggest a work around please?

Best Answer

The code is not valid MATLAB unless SignalIndex is either a scalar number or else a logical array that is certain to have exactly one true in it.

Break the code into two parts. In the first part, do the structure indexing and assign the selected scalar structure to a variable. In the second part access the appropriate field of the scalar structure.

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MATLAB: Scalar vs nonscalar structure: advantages

What you want to do with your data? This documentation page gives two examples that show how each type of struct allows you to "slice" your data in a different way.

In the first example (the RGB image) accessing all the data in one color plane is easy while accessing all the data for a single pixel across the three planes is more involved.

In the second example (the patient data) accessing all the data for one patient is easy while accessing a particular piece of data for all patients is more involved.

I would like to point out one alternative that may be a better fit for your needs. If you have data arranged as a rectangular table consider storing it as a table array or a timetable array. If you look at the examples on the table documentation page you can see that you can access all data for a particular patient (in the "Specify Row Names" example) or all of a particular type of data for each patient ("Store Related Data Variables in Table") through one indexing expression.

MATLAB: Accessing timer UserData fields

Interesting, I had never seen that message before.

The work-around is

getfield(t.UserData, 'field1')

Best Answer

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