If I have a logical vector created by ISDIR attribute of DIR, how to have its order by the date of the last modification of folders???

d = dir('D:\= BIO-PD =');
isub = [d(:).isdir]; %# returns logical vector
nameFolds = {d(isub).name}';

In nameFolds I have a cell array with the names of folders contained in 'D:\= BIO-PD ='.

The problem is I need to have nameFolds sorted by the date of the last change of the folders, as it is located in the real folder.

[Walter Roberson]

Look at the second output of sort, and use that to reorder the other content

[Kapa Kudaibergenov]

Can you explain me how we use it in this case? Do you mean to use it like:

[B,I] = sort(nameFolds)

Answer 1

[Stephen23]

Simpler and much more robust:

S = dir('D:\= BIO-PD =');
S = S([S.isdir] & ~ismember({S.name},{'.','..'})); % folders only, exclude '.' and '..'
[~,X] = sort([S.datenum]); % sort datenum
N = {S(X).name} % folder names in datenum order

[Kapa Kudaibergenov]

Works excellent thanks)

Answer 2

[Image Analyst]

Try this.

files = dir('*.*')
areAFolder = [files.isdir]
files = files(areAFolder) % Get folders only, not files.
% Get rid of dot and dot dot folders.
if length(files) >= 3
	% Assume they are the first two entries.  Remove them.
	files = files(3:end);
% 	% OR Alternate way that does not depend on them being the first two.  Comment out the line above if you use this method.
% 	[ia, ib] = ismember({'..'}, {files.name})
% 	files(ib) = [];
% 	[ia, ib] = ismember({'.'}, {files.name})
% 	files(ib) = [];
end
[fileDates, sortOrder] = sort([files.datenum], 'descend') % or 'ascend' - whatever you want.
folders = files(sortOrder)

Adapt as needed.

[Stephen23]

Code which assumes that the dot drectory names always exist and are always in the first two elements of the structure should be avoided, because:

1. Changes to the dir search string can result in different outputs which may or may not contain the '.' and '..' strings. This code will silently remove names of actual files/folders without warning.
2. It is easy to demonstrate file/folder names where those names are NOT the first two elements:

>> fclose(fopen('+test.txt','wt'));
>> fclose(fopen('-test.txt','wt'));
>> fclose(fopen('@test.txt','wt'));
>> S = dir('*');
>> S.name
ans = +test.txt
ans = .test.txt
ans = .
ans = ..
ans = @test.txt

This topic has been discussed extensively on this forum:

https://www.mathworks.com/matlabcentral/answers/484430-using-struct-dir-selpath-what-do-and-mean-as-struct-name#answer_395754

https://www.mathworks.com/matlabcentral/answers/40949-omitting-pointers-when-listing-folder-contents#answer_50568

https://www.mathworks.com/matlabcentral/answers/13978-list-of-files-sorting#answer_19278

As Walter Roberson wrote in that last link: "In short: if your code assumes that '.' and '..' are the first two entries in a directory, your code has a bug (even in MS Windows). If your code assumes that directory entries are returned in any sorted order, your code has a bug (in all OS.)"

[Image Analyst]

So then uncomment the lines and use ismember() just like you did.

files = dir('*.*')
areAFolder = [files.isdir]
files = files(areAFolder)
% Get rid of dot and dot dot folders.
% Does not assume they are the first two entries.  Remove them.
[~, ib] = ismember({'..'}, {files.name})
files(ib) = [];
[~, ib] = ismember({'.'}, {files.name})
files(ib) = [];
[fileDates, sortOrder] = sort([files.datenum], 'descend')
folders = files(sortOrder)

My ismember code is essentially the same as yours, though not as compact because I use longer, more descriptive variable names and am not combining multiple operations into a single line of code, a coding style that I use because I think it's easier for beginners to follow.

Since I've never seen in Windows where the dot and dot dot were not the first files returned by dir(), can you tell me how that might occur? Since a folder must exist before a subfolder is created, and a folder must exist before a file is created in it, I'm curious how a file would get a date before the file? Does it depend on which date is being returned by dir()? I know that Windows has several dates, created date, modified date, and accessed date, and maybe more. If a file is moved or copied into an existing folder, some dates are retained and some are reset when a file is copied/moved into a folder.

[Stephen23]

"Since I've never seen in Windows where the dot and dot dot were not the first files returned by dir()"

I have seen this with files I received from colleagues, so this is not just a hypothetical bug.

"... can you tell me how that might occur?"

Did you try actually reading my last comment? In it I gave a working example.

"Since a folder must exist before a subfolder is created, and a folder must exist before a file is created in it, I'm curious how a file would get a data before the file?"

I have no idea what that means, but as it does not seem to be related in any way to the topic that I was disscussing, I will presume that your question is aimed at someone else.

"My ismember code is essentially the same as yours, though not as compact because I use longer, more descriptive variable names and am not combining multiple operations into a single line of code, a coding style that I use because I think it's easier for beginners to follow"

That... and the difference that your code includes a major bug based on incorrect assumptions.

[Image Analyst]

Alright Stephen. You're right, I'm wrong. Thank you for showing that if the filename starts with an ASCII character coming before dot, that it will get returned in the alphanumerical list before dot and dot dot. I can delete my Answer if you want. No hurt feelings. ?

[Walter Roberson]

I have not tested far enough in Windows to determine how NTFS sorts filenames in practice. For example if the user used U+0308 (combining diaerisis) followed by lower case o then will NTFS canonicalize as ö U+00F6? Will it use utf8 and sort as 0xCC 0x88? Will it use utf16 little endian and sort as 0x08 0x03? Will it use utf16 big endian and sort as 0x03 0x08? Will it sort by the 8+3 surrogate name?

[Image Analyst]

I think if you sorted by date before removing the dot and dot dot, then they should always be the first two in the list, because as far as I know they must always be the oldest (unless it's something to do with Windows multiple dates policy). That's what I had intended to do, but didn't. But of course checking the name directly is more robust.

[Walter Roberson]

The field returned by dir() is modification date, and modification date of a directory reflects the most recent time a file was added or removed from the directory. That would tend to sort . at the end possibly some distance from ..