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How to use array indexing with input dialog

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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 Comment
Tony
Tony on 21 Jun 2024
I think it would help to give more details, such as some example lines of code

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Accepted Answer

Pavan Sahith
Pavan Sahith on 21 Jun 2024
Edited: Pavan Sahith on 21 Jun 2024
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
Hope this helps you getting started
  2 Comments
Pavan Sahith
Pavan Sahith on 6 Aug 2024
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.

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