Arrays have incompatible sizes for this operation error while checking dropdown.value not equal to a char value

I have created an app in appdesigner and it has a dropdown. And I check the value of this dropdown to a string value.

function SelectBatteryDropDownValueChanged(app, event)
    if app.SelectBatteryDropDown.Value ~= 'none'
    end
end

'none' is one of the values initialised to the dropdown. Now a select a value from the dropdown I expect the program to check first if the value is not equal to 'none' and if true execute some code. But It is giving an error :

Arrays have incompatible sizes for this operation.

This doesnt make any sense since both 'none' and app.SelectBatteryDropDown.Value are of type char, I checked to make sure. Yet this error is coming. Why is that? How can I fix this. Thank you.

Answer 1

[Voss]

Don't use == or ~= to compare character arrays, use strcmp, i.e.:

if ~strcmp(app.SelectBatteryDropDown.Value,'none')

because == and ~= perform element-by-element comparison (just as they do with numeric arrays), which in the case of comparing character arrays, is comparing character by character, e.g.:

'some' == 'none' % compares each character in 'some' to the corresponding character in 'none'

ans = 1x4 logical array
   0   1   0   1

'ok' == 'none' % cannot element-wise compare a two-element character vector with a four-element one

Arrays have incompatible sizes for this operation.

https://www.mathworks.com/help/matlab/ref/strcmp.html

[Voss]

An alternative is to make one or both of the character arrays into string objects, and then you can use == or ~=, i.e.:

if string(app.SelectBatteryDropDown.Value) ~= 'none'

[Govind Sankar Madhavan Pillai Ramachandran Nair]

Thank you very much, it worked

[Voss]

You're welcome!