Editor's Note: This file was selected as MATLAB Central Pick of the Week
Natural order sorting sorts strings containing digits in a way such that the numerical value of the digits is taken into account. It is especially useful for sorting file names containing index numbers with different numbers of digits. Often, people will use leading zeros to get the right sort order, but with this function you don't have to do that. For example, with input of
{'file1.txt','file2.txt','file10.txt'}
a normal sort will give you
{'file1.txt','file10.txt','file2.txt'}
whereas, sort_nat will give you
{'file1.txt','file2.txt','file10.txt'}
Douglas Schwarz (2020). sort_nat: Natural Order Sort (https://www.mathworks.com/matlabcentral/fileexchange/10959sort_natnaturalordersort), MATLAB Central File Exchange. Retrieved .
1.3.0.0  Fixed bug identified by Evgeny Pr. (Thanks!) 

1.2.0.0  Added ability to sort in descending order. 

1.1.0.0  Steve Herman identified an obscure bug (sorting a cell array of one string which has no numeric characters) which has now been fixed. Thank you Steve! 

1.0.0.0  Fixed ambiguity of sort order in certain cases e.g., {'a0','a00'}. Increased speed. Relaxed MATLAB version requirements  no longer requires R2006a, should work with much older versions now. 
Inspired: Depth of field calculator based on 2D digital image correlation data, Customizable NaturalOrder Sort, philipptempel/matlabprojectmanagement, NaturalOrder Row Sort, NaturalOrder Filename Sort, Lilo : Fast and pixelaccurate stitching for 2D tiles, KANTOO, DETEQT
Create scripts with code, output, and formatted text in a single executable document.
Well done, thanks a lot!
Great Work,
It will solve many issues in image processing application developement.
Thanks very muck !!!!
非常感谢，看似简单的处理，但是却解决了让人很头疼的问题！！
Great submission, and it is a must in many of my scripts. If you happen to need to use this for strings with decimals in them, you can try to replace the regex '\d+' with '\d+(?:\.\d+)?', for example the current version does this:
A = { '1.test', '10.test', '2.test', '1.3.test' }
sort_nat(A)
ans =
1×4 cell array
'1.3.test' '1.test' '2.test' '10.test'
But with the change you get '1.test' '1.3.test' '2.test' '10.test'.
^^Thank you soooooo much! It should be a required function for Matlab.
Very useful, thanks!!
This is a fantastic utility. Thanks!
Super handy
Thanks Douglas
Antonio, this page is for my submission, sort_nat. natsort and natsortfiles are submissions from another author. Search for them.
I am working with 2016a Matlab version and I don't find this function: natsort, natsortfiles
Help please!!!!!!!!!
Very useful! Thank you!
Thanks!
Exactly what I needed, great tool! Thanks a million! :)
exactly what I needed!
Thank you sooo much :)
Nice and Tidy!
a very nice tool, thanks!
perfect, thanks. Have a nice day :)
eFKa, sort_nat requires a cell array of strings. You can do what you want like this:
[~,order] = sort_nat({files.name});
files_sorted = files(order);
We are using the second output to get the order and then applying that order to your original structure.
Doug
i have a 50x1 struct called files and a field called name like so
'10up.txt'
'11up.txt'
.
.
.
'19up.txt'
'1up.txt'
how do i use sort_nat(files.name) gives me error saying "too many input arguments"
Thanks!!
Excellent! Works flawlessly, saved some time of an electronic engineer. Thank you!
Sorting filenames using a sort function such as "sort_nat" can return nonuserintuitive ordering, as some longer filenames will sort before shorter filenames. This is due to char(0:45), including [ !"#$%&'()*+,], sorting before the period '.' (char(46) used as the extension separator. For example:
fnm = {...
'test2.m';
'test.m';
'test10.m';
'test1.m';
'testA.m';
'test_A.m';
'test10old.m'};
% "sort" gives the wrong order for numeric substrings:
sort(fnm)
ans = {...
'testA.m';
'test.m';
'test1.m';
'test10old.m';
'test10.m';
'test2.m';
'test_A.m'}
% "sort_nat" gives numeric substrings in the correct order, but with '' before '.':
sort_nat(fnm)
ans = {...
'testA.m';
'test.m';
'test1.m';
'test2.m';
'test10old.m';
'test10.m';
'test_A.m'}
% Note how 'testA.m' occurs before the shorter named 'test.m', and likewise 'test10old.m' before 'test10.m'. Users expecting shorter filenames to sort before longer ones need to sort using a different algorithm...
One solution is to sort the filename and file extensions separately, for which I wrote a function "natsortfiles":
natsortfiles(fnm, '\d+', 'beforechar')
ans = {...
'test.m';
'test1.m';
'test2.m';
'test10.m';
'test10old.m';
'testA.m';
'test_A.m'}
It allows control over case sensitivity, sort direction, and numeric substring matching. You can find this function on FEX here:
http://www.mathworks.com/matlabcentral/fileexchange/47434
It also accepts fullpaths, for which it sorts each level of the directory hierarchy separately too.
Thank you very much. It is in the same folder. This is why I am very surprised.
Maryam, make sure that sort_nat.m is in a folder that is on your MATLAB path. You can read more about the path with "doc path".
Hello. I wan to use this program to sort a vector a strings which have numerical values in their name. I am giving this error: Undefined function 'sort_nat' for input arguments of type 'cell'
what should I do?
Sergey,
Well, it's not a bug, but you might disagree with my logic. Remember, we are sorting strings, not numbers. '01' comes after '1' because they have the same numerical value, but '01' is a longer string. Likewise, '000' comes after '00', etc.
It may be possible to include '+.,' by changing the regular expressions (currently just looking for runs of digits with '\d+'.
Very fast! I can't beat it!
This might be a bug though, not sure?
sort_nat({'01E2' '1E3'})
ans = '1E3' '01E2'
I came up with a version that can treat '+.,' as part of the number, but its 10x slower. Not sure if sort_nat can be extended to do same.
thank you very much!
i was typing C=[list.name] and not
C={list.name} which is the right.
thank you very much again!
very usefull function!
Alex, your input has to be a cell array:
>> C = {'1.bmp','10.bmp','11.bmp','2.bmp'};
>> sort_nat(C)
ans =
'1.bmp' '2.bmp' '10.bmp' '11.bmp'
i find this very useful,but i cant use it.
C =
1.bmp10.bmp11.bmp2.bmp
>> [S,INDEX] = sort_nat(C)
Cell contents reference from a noncell array object.
Error in sort_nat (line 62)
num_val(i,z(i,:)) = sscanf(sprintf('%s ',digruns{i}{:}),'%f');
any help?
Very useful  worked was described! Thanks.
It work well and help a lot. So awesome!!!
Thank you
Thank you so much, saved me a lot of time! Dirk
Sorry, I am a beginner in MATLAB and I am not sure what the input arguments in these function mean. There are many input argument.... I have a struct array (conists of files with names ex.123_1, 123_2, etc) A <3000*1> struct and I want to sort it according to name of files which are there. How shoud I use this function... Please help me.. best wiches Katya
thanks a lot!!! great
Excellent
Just what I needed, thanks!
I have wasted a lot of time trying to properly sort my image files for my image processing project before I surfed on to this code. And mathworks web tutorial on this is totally flawed. Great work! Certainly deserves a 5 star.
Excellent work. Saved me a much time and headache with some data analysis over here at NASA. Thank you!
This is great! Better to include it in the Matlab!
Many thanks, save me time and effort to write my own code to crack this problem
Great, works straight off in Octave too.
Douglas Schwarz,
You offered the perfect solution for caseinsensitive sorting.
Thank you!
Evgeny, you must be the first person to use descending order and the index. You are quite right, it's a bug and I thank you for identifying it. I fixed it in a slightly different way and just uploaded the new version.
To do caseinsensitive sorting you can just do this:
c = {'a1', 'a2', 'a10', 'b1', 'X1', 'A10'};
[unused,index] = sort_nat(lower(c));
cs = c(index);
I want sort_nat to work the same way as sort and since sort doesn't do caseinsensitive sorting I left that out of sort_nat as well.
Regards,
Doug
This code not entirely correct:
if strcmpi(mode,'ascend')
cs = c(index);
else
cs = c(index(end:1:1));
end
Output argument INDEX does not change depending on the sort order.
Better to do so:
if strcmpi(mode, 'descend')
index = flipud(index);
end
cs = c(index);
index = reshape(index, size(cs)); % same as C array dimension
Hi! Very good function and coding!
I could not write such a elegant and fast function. :)
One question:
You would not want to make sort mode a caseinsensitive?
For Example:
c = {'a1', 'a2', 'a10', 'b1', 'X1', 'A10'}
Casesensetive sort:
cs = {'A10', 'X1', 'a1', 'a2', 'a10', 'b1'}
Caseinsensitive sort:
cs = {'a1', 'a2', 'a10', 'A10', 'b1', 'X1'}
Excellent. 5 stars.
I think I ran into the need for a descending sort because I was looking to search through various files with timestamps in their name for the most recent entry (of somethingorother).
Anyway, good work.
Pete, I'm not sure sorting in descending order will be used very often, but, as you say, it's easy to add so why not? I chose to do it in a slightly different way, but it works the way you want. Thanks for the suggestion. Update should appear soon.
Good work.
Is it just me though or would this not benefit from being able to specify the direction? This would be as simple as:
function [cs,index] = sort_nat(c,varargin)
... <entire code>
if nargin>1
if strcmpi(varargin{1},'descend')
index = flipud(index);
cs = c(index);
end
end
I wish I'd found this sooner!
Nifty, thanks.
Thanks
Nice! Thanks
Great, just what I needed.
Perfect. Should be included in R2007a!
Great, much better than another file on the exchange "sortn", sortn froze when trying to sort over 6000 strings, this sort did it just fine in about a second.