How to use array indexing with input dialog

Dear MatLab Community, I am trying to use input dialog for indexing my array. The indexing is not a problem with numbers, however, when I try to give 1:end as default answer, the behavior of str2double I do not understand, and it does not work for me.

Any suggestions are highly appreciated.

Thank you

lg

e.g

a=1:100;

prompt = {'Enter timeframe:'};

dlg_title = 'Input';

num_lines = 1;

defaultans = {'1:end'};

answer = inputdlg(prompt,dlg_title,num_lines,defaultans);

a=a(1,str2double(answer{1, 1}));

so, how to use 1:end or something:something in the input dialog to get the wished length of variable a?

[Tony]

I think it would help to give more details, such as some example lines of code

Answer 1

[Pavan Sahith]

Hello Leventte,

I see that you are encountering issues when trying to accept expressions like 1:end from an input dialog in MATLAB.

The str2double function is designed to convert strings to numeric values and doesn't interpret MATLAB expressions like 1:end. To handle this, you can use eval to evaluate the input string as a MATLAB expression.

I assume your usecase is to fetch array indices from the input dialog , so you can refer to this sample code to understand the usage of eval

a = 1:100;
prompt = {'Enter timeframe:'};
dlg_title = 'Input';
num_lines = 1;
defaultans = {'1:end'};
answer = inputdlg(prompt, dlg_title, num_lines, defaultans);

% Check if the user provided an input
if ~isempty(answer)
    try
        % Evaluate the indexing expression
        indexExpression = answer{1};
        index = eval(['a(' indexExpression ')']);
        disp('Indexed values:');
        disp(index);
    catch ME
        % Handle any errors that occur during evaluation
        disp('Error evaluating indexing expression:');
        disp(ME.message);
    end
else
    disp('No input provided.');
end

you can refer to the following MathWorks documentation to know more about

eval-https://www.mathworks.com/help/matlab/ref/eval.html

Hope this helps you getting started

[Ganesh]

@Levente Gellért, you should also be aware of the risks with using "eval()"

https://www.mathworks.com/help/matlab/matlab_prog/string-evaluation.html

[Pavan Sahith]

yeah true, using eval in MATLAB can pose significant security risks, especially when dealing with untrusted input.

To mitigate these risks, one of the way is to combine try-catch blocks with input validation, as demonstrated in the code above.

Additionally, you can explore safer alternatives to eval.

Alternatives to the eval Function: https://www.mathworks.com/help/matlab/matlab_prog/string-evaluation.html