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.
