Issue with length function

Question

julian gaviria 2022-3-14

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1671129-issue-with-length-function

评论： Rik 2022-3-14

Why does the length function never stops the iteration?

Context: Using copyfile function (matlab2018b) for copying and pasting indexed files. To note, the files are rightly copied and pasted. But the iteration never ends. Even if Idelet the files in the destination folder, it keeps pasting them.

%%% 
clc
clear
SourcePath ='\\nasac-m2.isis.unige.ch\m-GAubry\GAubry\YODA\RAW_DATA\Live\S008\V1\';       
Participant = 'Session_2\scans\87627';
SourceFolder = fullfile([SourcePath,Participant],'RUN_1_MIST_1_0004');
DistPath ='\\nasac-m2.isis.unige.ch\m-GAubry\GAubry\YODA\jg\prp_glm\Sub_08\';
DistFolder = fullfile(DistPath,'FunRaw_S1');
if ~exist(DistFolder)
    mkdir(DistFolder)
end
for i=1:length(dir(fullfile(SourceFolder,'f*')))
    copyfile(fullfile(SourceFolder,'f*'),DistFolder);
end

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Answer 1

Geoff Hayes 2022-3-14

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https://ww2.mathworks.cn/matlabcentral/answers/1671129-issue-with-length-function#answer_917119

在 MATLAB Online 中打开

@julian gaviria - why aren't you using the i in your loop?

for i=1:length(dir(fullfile(SourceFolder,'f*')))
    copyfile(fullfile(SourceFolder,'f*'),DistFolder);
end

So it would seem that the above code would try to copy the full set of files for every file in the directory that matches the condition. Perhaps the following might help

filesToCopy = dir(fullfile(SourceFolder,'f*'));
for i=1:length(filesToCopy)
    copyfile(fullfile(SourceFolder,filesToCopy(i).name),DistFolder);
end

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julian gaviria 2022-3-14

在 MATLAB Online 中打开

It worked, Thanks @Geoff Hayes & @VBBV

the Line suggested by @VBBV were simpler:

copyfile(fullfile(SourceFolder,'f*'),DistFolder);

Just for learining porpuses:

As @Geoff Hayes rigthtly mentioned, my code tried to copy the full set of files for every file in the directory that matches the condition:

for i=1:length(dir(fullfile(SourceFolder,'f*')))
    copyfile(fullfile(SourceFolder,'f*'),DistFolder);
end

Why matlab never ended the iteration in this case? I see no misuse of the "length" function.

Thank you all again for your help.

Best,

Rik 2022-3-14

You may not see a misuse, but I'm of the opinion you should see a bad habit. Did you intend the number of elements? Then you can more reliably get that with numel. Did you really want max(size(X))? I have never seen anyone who actually wanted that.

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