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

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Govind Sankar Madhavan Pillai Ramachandran Nair 2024-7-16

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https://ww2.mathworks.cn/matlabcentral/answers/2137688-arrays-have-incompatible-sizes-for-this-operation-error-while-checking-dropdown-value-not-equal-to-a

评论： Voss 2024-7-16

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.

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Answer 1

Voss 2024-7-16

编辑：Voss 2024-7-16

在 MATLAB Online 中打开

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.