When the variable name is changed, it gives error

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Shaya s 2017-8-7

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评论： Shaya s 2017-8-7

Hello,

I'm trying to calculate the duration of some certain episodes including "Exp" and "ExpN" in an audio signal. There's a weird problem that when I change the variable name it doesn't result. Will you take a look at below codes (the error is for the last line for "ExpN_sum_duration"):

   dataset_root='C:\datasets\dataset_Experiment1\segments_all\...';
   Exp_root=dir(fullfile(dataset_root,'EXP*.wav'));
   Exp_no=numel(Exp_root);
   for i=1:Exp_no
        info=audioinfo(fullfile(dataset_root,Exp_root(i).name));
          duration_Exp(i)=info.Duration;
    end
    Exp_sum_duration= sum(duration_Exp)
    %------------------------------------------------------------
    ExpN_root=dir(fullfile(dataset_root,'EXPN*.wav'));
    ExpN_no=numel(ExpN_root);
    for ii=1:ExpN_no
        info=audioinfo(fullfile(dataset_root,ExpN_root(ii).name));
          duration_ExpN(ii)=info.Duration;
     end
     ExpN_sum_duration= sum(duration_ExpN)

So as you see there are two parts. In the first part I get the result of the "Exp_sum_duration", whereas for the next part I receive error for "ExpN_sum_duration", which is:

Undefined function or variable 'duration_ExpN'.

     Error in Exp_percent_test (line 28)
     ExpN_sum_duration= sum(duration_ExpN)

Thanks for reading.

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Stephen23 2017-8-7

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Question: what function does the ellipsis have?:

'C:\datasets\dataset_Experiment1\segments_all\...'

Shaya s 2017-8-7

Sorry, I don't understand your question. If you mean about the address, I had deleted the ending part of it because it was long.

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Answer 1

Stephen23 2017-8-7

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https://ww2.mathworks.cn/matlabcentral/answers/351852-when-the-variable-name-is-changed-it-gives-error#answer_277116

编辑：Stephen23 2017-8-7

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I bet if you looked at the value of ExpN_no it is zero.

The cause will be that there are no files matching that pattern in that directory:

ExpN_root=dir(fullfile(dataset_root,'EXPN*.wav'));

therefore numel returns zero:

ExpN_no=numel(ExpN_root);

and so the loop iterates exactly zero times

for ii=1:ExpN_no

and so the variable duration_ExpN, which is only defined inside that loop, is never defined. Your code is very fragile because it cannot handle highly predictable situations, such as files not being found. To write robust code you have to think not just about "what should my code do in nominal mode", but also "what should my code do when something does not exist / is not loaded / has an invalid value / is corrupted / etc etc".