Check if a value from a dropdown menu is in a struct

Hi. I have the following code, where I struggle because no member is detected.

My 'idx' just return a 1*80 logical containing zeros. When I debug I can see that 'a' contains 16 doubles with the number 67.2022 and 'b2' is a double variable with the number 67.2022. So the are both the same type.

            a = [app.sortedS.SliceLocation]; % this is a column from a struct containing different double values 
            b = app.dd_SliceLocation.Value; % this is a value from a dropdown box 
            b2 = str2double(b); 
            for ii = 1:length(a)
            idx(ii) = ismember(b2,a(ii));
            end 
            imageT = app.sortedS.Image(idx) % Image is a column in the same struct (sortedS) as 'a'.            

Hope you are able to help!

Answer 1

[Stephen23]

Most likely those values are not exactly the same because you are trying to compare floating-point numbers, which is never a good idea, as has been discussed countless times already on this forum:

https://www.mathworks.com/matlabcentral/answers/423132-why-is-matlab-messing-up-this-very-simple-calculation#answer_340581

https://www.mathworks.com/matlabcentral/answers/272092-basic-indexing-question-find-ismember#answer_212787

You can easily resolve this using ismembertol

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

or compare the absolute difference against a tolerance:

abs(A-B)<tol