How to use "dir"?

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SM 2020-9-21

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编辑： Stephen23 2020-9-21

I have 45 folders with name Inst1, Inst2, Inst3,Inst4,........Inst45. I use a command of

finfo=dir('Inst*');

The outcome should come in ascending order of folders but it comes random. How can I solve the problem?

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Stephen23 2020-9-21

编辑：Stephen23 2020-9-21

"The outcome should come in ascending order of folders..."

I don't see it documented anywhere that any particular order "should" be returned by dir.

"...but it comes random."

Not random, most likely sorted by character order. You can sort them alphanumerically if you want:

https://www.mathworks.com/matlabcentral/fileexchange/47434-natural-order-filename-sort

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Answer 1

per isakson 2020-9-21

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Renam the folders 'Inst1', to, 'Inst01', etc. or see natural order.

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Walter Roberson 2020-9-21

Renaming the folders with leading 0s on the numbers will probably work, but it is not guaranteed.

dir() is not formally defined to return any particular order: the order returned is whatever the operating system returns.

In turn, in MS Windows, Mac, and Linux, the underlying directory filesystem operation is not defined to return any particular order: the order depends upon what the filesystem layer returns.

Mac and Linux filesystems document the order of files -- though in some cases the defined order is "whatever happens to work out in the b-trees".

I have not found any formal definition of the order for NTFS file system. In practice for characters up to char(255) it sorts in order by character value. I have not seen any formal definition for NTFS sorting order for unicode characters.

POSIX formally defines sorting rules, but it also formally defines that the sorting rules are to be influenced by the user's LOCALE settings, so the order is not always the same between different users. For example in Spanish, ñ should sort after n but before o .

All of which is to say that if you need the files to be arranged in a particular order that is different from "whatever the filesystem and operating system agree on" then you should use a filename sorting routine.

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