How to loop through a folder?

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andrew
andrew 2014-3-11
评论： Image Analyst 2020-12-10
I currently have 24 folders within a folder and I was wondering if it was possible to loop through the 24 folders and extract information from a subfolder within the 24 folders.
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Brando Miranda
Brando Miranda 2018-3-30
great question. This is some of the trivialest things to do in a language and its incomprehensible how hard it is to do in matlab.

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回答（3 个）

Image Analyst
Image Analyst 2014-3-11
See my attached demo where it recurses through a folder and all subfolders.
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Rik
Rik 2020-12-10
You can use the ** option of dir. What did you try?
Image Analyst
Image Analyst 2020-12-10
Yes, essentially it's
filePattern = sprintf('%s/**/*.*', topLevelFolder);
allFileInfo = dir(filePattern);
See my attached m-file for a full demo with tons of explanations.

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Sean de Wolski
Sean de Wolski 2014-3-11
编辑：Sean de Wolski 2014-3-11
You can use the dir command to give you the names and then loop over them.
files = dir;
directoryNames = {files([files.isdir]).name};
directoryNames = directoryNames(~ismember(directoryNames,{'.','..'}))
Now run the for-loop over directoryNames and apply your analysis to each
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Brando Miranda
Brando Miranda 2018-3-30
why does
directoryNames = {files([files.isdir]).name};
work? its really cryptic? are u using list comprehensions or what dark magic is going on there?
Stephen23
Stephen23 2018-3-30
编辑：Stephen23 2018-3-30
@Brando Miranda: "list comprehensions" exist only in Python. They do not exist in MATLAB.
The syntax in both your comments uses comma-separated lists. Comma-separated lists are very simple:
https://www.mathworks.com/matlabcentral/answers/320713-how-to-operate-on-comma-separated-lists

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manideep reddy
manideep reddy 2018-4-18

see my code below but make sure that the folder which we are looping through contains only flolders and not files.

 cd pwd ; ## Or any other working directory you want
X = ls  ;
disp(X) ;
for itr = 1:size(X)(1)
	string_1 = X(itr,:) ;
	string_2{itr} = deblank(string_1) ;  ## This deletes the trailing blank spaces 			
end
for itr = 1:size(X)(1)
	cd(string_2{itr})
	cd ../
	# DO SOMETHING #
end
  end
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Stephen23
Stephen23 2018-4-18
编辑：Stephen23 2018-4-18
This code has several bugs and could be significantly improved:
  • Do NOT use cd. Using cd is slower than using absolute/relative filepaths, makes debugging more difficult, and changes which functions/scripts are accessible to MATLAB. It is NOT necessary to cd directories where datafiles are stored because all MATLAB filereading/writing functions accept relative/absolute paths. Basically cd should only be used interactively, and NOT used in code. See:
https://www.mathworks.com/matlabcentral/answers/247272-problem-with-change-directory-in-a-for-loop
https://www.mathworks.com/matlabcentral/answers/376645-how-to-use-a-function-that-is-not-in-the-same-folder-as-your-current-folder
https://www.mathworks.com/matlabcentral/answers/380704-access-parent-folder-when-using-a-directory-junction
https://www.mathworks.com/matlabcentral/answers/376645-how-to-use-a-function-that-is-not-in-the-same-folder-as-your-current-folder
https://www.mathworks.com/matlabcentral/answers/112086-matlab-slow-when-too-many-files-in-directory
  • Do NOT use ls for parsing filenames. This operator is intended for displaying a list in the command window, but parsing its output char array is a waste of time. dir is what the MATLAB documentation recommends and shows in all examples that require reading multiple files from a folder, e.g.:
https://www.mathworks.com/help/matlab/import_export/process-a-sequence-of-files.html
https://www.mathworks.com/matlabcentral/answers/379892-why-does-ls-add-trailing-space-preventing-output-use-as-filename-string#answer_302628
  • size(X)(1) is not valid MATLAB syntax, and will throw an error.
  • string_2 is not preallocated.
  • A loop is anyway not required for deblanking the filenames: simply use deblank(cellstr(X)).
Rather than following this buggy code, I recommend that other users follow the examples shown in the MATLAB help and wiki:
https://www.mathworks.com/help/matlab/import_export/process-a-sequence-of-files.html
http://matlab.wikia.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F
manideep reddy
manideep reddy 2018-4-20
Thank you very much. I am actually not a computer science student. So, just answered the query without considering algorithm and complexity. Anyway, I will implement your suggestions/ recommendations in future. Thanks..!

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