How to get rid of Warning"Unexpected use of '[' in a scalar context."

a part of the function has:

if the input A (a vector) matches what is stated, the statement runs.

   if A == [1,3,3]
      % statement
    end

and it gives me this error: 'Unexpected use of '[' in a scalar context. How can I fix this?

[dpb]

Must be more than that; that code runs w/o any error here...

>> A=3;
>> if A==[1, 3, 3],disp('ok'),end
>> A=[1 3 3];
>> if A==[1, 3, 3],disp('ok'),end
ok
>>

Show us the context including the error message with all the text generated...

[Crystal Lee]

There is no red text, I was just wondering if I could get rid of the orange warning.

Answer 1

[Stephen23]

Use all or any, like this:

if all(A==[1,3,3])

Or right-click the pop-up warning box and follow the instructions to suppress it.

[Crystal Lee]

Thank you!

[Thiago Rodrigues]

What the explanation for the "all" fix the warning?

[Stephen23]

"What the explanation for the "all" fix the warning?"

Given a vector input the output from all is scalar. A scalar condition is easier to understand, which is why it is recommended by that warning.

Answer 2

[KSSV]

When you use A == [1 3 3] ;

With this operator ==, MATLAB expects a scalar value, but the way used here, it gives array as output. So the warning pops out. The way you use, won't work out. YOu need to use the operator == with a scalar value, so the if condition works fine.

[Stephen23]

"With this operator ==, MATLAB expects a scalar value..."

Can you please provide a reference to the MATLAB documentation, where this is stated?

According the eq help it accepts inputs that are "scalar | vector | matrix | multidimensional array". Every time I have used == with non-scalar input arguments it worked as expected.

"YOu need to use the operator == with a scalar value, so the if condition works fine."

The non-scalar if condition works for me, without any problems:

>> if [2,3,99]==[2,3,99], disp('hello'), end
hello
>>

Of course that if condition will only be considered true for non-scalar inputs when all elements of the condition are non-zero, but that is not what you have written in your answer. Perhaps suggesting any or all might have been useful.

[KSSV]

Check the image.

[Stephen23]

Aha, thank you KSSV. This is a new warning (not an error, as the question states), that must have been introduced with some new MATLAB version. May I ask what version you are using?

Note that this issue is not because "With this operator ==, MATLAB expects a scalar value", but is because if expects a scalar value: if expects the scalar, not ==.

Also "YOu need to use the operator == with a scalar value..." is not correct: a simple all, any, etc would solve this quite easily, as my answer shows, by providing the scalar that if expects.

[KSSV]

Yes....it is not a error..it is a warning....I am using 2015b.

[Crystal Lee]

Sorry, I confused warning with error.

Answer 3

[David]

You may want to use isequal instead of == for that use case.