Good practice in conditional test with categorical variable
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Xiaoxing Zhang
on 26 Mar 2023
Commented: the cyclist
on 29 Mar 2023
So I defined a categorical variable and tested its value in a conditional statement using the "==" operator, as seen in the image. The program works OK, thus I'm guessing such syntax is acceptable. But I kept getting warnings like the one in the image in the MATLAB IDE. How can my code be changed so that the warning is suppressed, and what is the underlying explanation for what is and is not a good practice when dealing with categorical variables in a conditional test?
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the cyclist
on 26 Mar 2023
Edited: the cyclist
on 26 Mar 2023
The reason you are getting this mlint warning isn't really about the categorical variables at all. It is because you are trying to make a vector comparison in the if statement.
'def' is a 1x3 character vector, so MATLAB is warning you that it is expecting an expression that will evaluate to a scalar in the if statement. It is akin to writing
if [2 3] == [5 7 11]
Now, it turns out that because MATLAB will do a conversion to compare your categorical variable to the character array
catvar = categorical({'def'},{'abc','def'});
if catvar == 'def'
fprintf("got here\n")
end
the syntax will work. (I don't know if it gives the result you intend, though.) In general, it's better not to rely on the conversion, but make it explicit. I don't know your broader context for wanting to use categorical variables overall, but this syntax would not give the warning.
catvar = categorical({'def'},{'abc','def'});
if catvar == categorical({'def'})
fprintf("got here, without mlint warning\n")
end
I do have the feeling that your whole situation might be easier if you used string arrays instead of categorical, but like I said, I don't know your broad context.
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the cyclist
on 29 Mar 2023
Between @Peter Perkins and me, we probably have nearly 60 years of MATLAB experience, so if we both suggested using strings arrays, you know it's a good idea. :-)
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