How to loop through a folder?

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.

[Brando Miranda]

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.

Answer 1

[Image Analyst]

See my attached demo where it recurses through a folder and all subfolders.

[N]

hi I love your code. I do have a question with it. If I would like to save the fullFileName, so it doesn't get overwritten every time, how would i do it?

[Image Analyst]

Make it a cell array

fullFileName{counter} = fullfile(thisFolder, baseFileNames(f).name);
counter = counter + 1;

[N]

If I do this, I get the error:

Cell contents assignment to a non-cell array object.

[Image Analyst]

Worked fine for me. See attachment.

[N]

thanks it works for me now too !

[Mor H]

Thanks a lot !

[Arantza Dobbels]

Hey guys! this is exactly the code that I need but for some reason when I try to run it, it says the number of folders is 1 and then says that there are no files in the subfolders. What am I doing wrong? Thanks!

[Vanessa Machuca]

I'm facing the same issue as Arantza. :(

[Image Analyst]

I made a newer one to use the new capabilities of dir() to use to recurse into subfolders. Try it. It's attached. Works for Release R2016b and later.

[Brando Miranda]

do you a non recursive version?

[Image Analyst]

Not sure what you're looking for. The program itself is not recursive - it uses the standard capability of the built-in dir() function. What I meant by recursive is that it finds files in folder, and in subfolders of those folder, and in subfolders of those subfolders, etc. until you've reached the deepest level of the directory tree.

What kind of problem are you having with the program such that you wanted to ask that question?

[Rik]

You can use the ** option of dir. What did you try?

[Image Analyst]

Yes, essentially it's

filePattern = sprintf('%s/**/*.*', topLevelFolder);
allFileInfo = dir(filePattern);

See my attached m-file for a full demo with tons of explanations.

Answer 2

[Sean de Wolski]

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

[andrew]

i'm just wondering how do you get the specific files within the folders of the directory names for example:

I need to get a csv file inside the directory of each directory name '\results\statistics*\.v2*' and print the filenames in a column

[Sean de Wolski]

Loop over the directory and use a wildcard inside of dir to grab all of the csv files. Something like

dir([directory '\*.csv'])

[andrew]

I used the following code and it says the file was not found:

for i=1:length(directoryNames)
  folder=directoryNames{i};
   filenames=dir([folder '\results\object statistics *.v2*'])

end

[Walter Roberson]

Note: fullfile() is better practice than concatenating file substrings.

And if you were to construct the specification as a variable you could then

ls(TheVariable)

to see if the files are found that way.

[Brando Miranda]

why does

    directories_names_list = dir('noise*')
    for expt_dir = directories_names_list.name

not work?

[Brando Miranda]

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]

@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

Answer 3

[manideep reddy]

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

[Stephen23]

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]

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..!