How to use array indexing with input dialog

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Levente Gellért
Levente Gellért 2024-6-21
评论： Pavan Sahith 2024-8-6
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?
  1 个评论
Tony
Tony 2024-6-21
I think it would help to give more details, such as some example lines of code

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Pavan Sahith
Pavan Sahith 2024-6-21
编辑：Pavan Sahith 2024-6-21
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
  2 个评论
Pavan Sahith
Pavan Sahith 2024-8-6
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

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