str2num strange behaviour

Dear, I have this code:

svmKernel ={'rbf','gaussian', 'linear','2','3','4'};
for k=1:numel(svmKernel)
    [p, status] = str2num(svmKernel{k});
    if ~status; t = templateSVM('Standardize',true,'KernelFunction',svmKernel{indK});                    
    else; t = templateSVM('Standardize',true,'KernelFunction','polynomial', 'PolynomialOrder', p); end        

WHY str2num returns p =

    Linear Function:
    Parameters: [1×1 struct]

and status = 1 when issuing [p,status] = str2num('linear')?

   [p, status] = str2num('linear')
Linear Function:
    Parameters: [1×1 struct]


status =

  logical

   1

[Bruno Luong]

Not for me.

>> [p, status] = str2num('linear')

p =

     []


status =

  logical

   0

IMO you overshadow stock function

[Elena Casiraghi]

Bruno thank you!

But How could I?

Do you have any idea?

[Bruno Luong]

type

which str2num

what do you see?

[Rik]

I would reccomend -all:

which str2num -all

That way you will see methods and shadowed functions as well. On my release (R2019a, only IPT and CFT installed) this returns:

>> which str2num -all
C:\Program Files\MATLAB\R2019a\toolbox\matlab\strfun\str2num.m
C:\Program Files\MATLAB\R2019a\toolbox\matlab\strfun\@opaque\str2num.m  % opaque method
C:\Program Files\MATLAB\R2019a\toolbox\matlab\bigdata\@tall\str2num.m   % tall method

[Elena Casiraghi]

Thanks!

This is a good information!

[Elena Casiraghi]

By the way, This is my result

which str2num
C:\Program Files\MATLAB\R2018a\toolbox\matlab\strfun\str2num.m

Answer 1

[Stephen23]

"str2num strange behaviour"

It is not strange behavior at all: str2num (unfortunately) relies on eval, as the str2num help clearly states "...str2num uses the eval function, which can cause unintended side effects when the input includes a function name." You provided str2num a function name to evaluate... you can easily find out which function it is evaluating:

which linear -all

As the str2num documentation recommends, you could avoid the whole problem simply by using str2double (which could be called before the loop), then using isnan.

[Elena Casiraghi]

Thanks Stephen!

[Steven Lord]

Another solution would be to avoid trying to convert that text data into numbers entirely.

svmKernel = {{'rbf'}, ...
    {'gaussian'}, ...
    {'linear'}, ...
    {'polynomial', 'PolynomialOrder', 2}, ...
    {'polynomial', 'PolynomialOrder', 3}, ...
    {'polynomial', 'PolynomialOrder', 4}};
for k=1:numel(svmKernel)
    t = templateSVM('Standardize',true,'KernelFunction', svmKernel{k}{:});
end

The command svmKernel{k} extracts the contents of each cell inside svmKernel in turn. Since I have cell arrays inside each of those cells, I can turn them into a comma-separated list. This is the technique shown in the "Function Call Arguments" example in the "How to Use the Comma-Separated Lists" item on that documentation page.

[Elena Casiraghi]

Tkanks Stephen!

I didin't know that! :)