自然排序算法介绍
Natural Order String Comparison
转载：http://sourcefrog.net/projects/natsort/
Computer string sorting algorithms generally don't order strings containing numbers in the same way that a human would do. Consider:
rfc1.txt rfc2086.txt rfc822.txt
It would be more friendly if the program listed the files as
rfc1.txt rfc822.txt rfc2086.txt
Filenames sort properly if people insert leading zeros, but they don't always do that.
I've written a subroutine that compares strings according to this natural ordering. You can use this routine in your own software, or download a patch to add it to your favourite Unix program.
Sorting
Strings are sorted as usual, except that decimal integer substrings are compared on their numeric value. For example,
a < a0 < a1 < a1a < a1b < a2 < a10 < a20
Strings can contain several number parts:
x2-g8 < x2-y7 < x2-y08 < x8-y8in which case numeric fields are separated by nonnumeric characters. Leading spaces are ignored. This works very well for IP addresses from log files, for example.
Leading zeros arenotignored, which tends to give more reasonable results on decimal fractions.
1.001 < 1.002 < 1.010 < 1.02 < 1.1 < 1.3
Some applications may wish to change this by modifying the test that callsisspace.
Performance is linear: each character of the string is scanned at most once, and only as many characters as necessary to decide are considered.
Licensing
This software is copyright by Martin Pool, and made available under the same licence as zlib:
This software is provided 'as-is', without any express or implied warranty. In no event will the authors be held liable for any damages arising from the use of this software.
Permission is granted to anyone to use this software for any purpose, including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions:
1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
3. This notice may not be removed or altered from any source distribution.
This licence applies only to the C implementation. You are free to reimplement the idea fom scratch in any language.
Related Work
POSIX sort(1) has the -n option to sort numbers, but this doesn't work if there is a non-numeric prefix.
GNU ls(1) has the--sort=versionoption, which works the same way.
The PHP scripting language now has astrnatcmpfunction based on this code. The PHP wrapper was done by Andrei Zimievsky.
Stuart Cheshirehas a Macintoshsystem extensionto do natural ordering. I indepdendently reinvented the algorithm, but Stuart had it first. I borrowed the termnatural sortfrom him.
Sort::Versionsin Perl. "The code has some special magic to deal with common conventions in program version numbers, like the difference between 'decimal' versions (eg perl 5.005) and the Unix kind (eg perl 5.6.1)."
Sort::Naturallyis also in Perl, by Sean M. Burke. It uses locale-sensitive character classes to sort words and numeric substrings in a way similar to natsort.
Ed Avis wrotesomething similar in Haskell.
Pierre-Luc Paour wrote aNaturalOrderComparatorin Java
Kristof Coomans wrote anatural sort comparison in Javascript
Alan Davies wrotenatcmp.rb, an implementation inRuby.
Numacomp- similar thing in Python.
as3natcompareimplementation in Flash ActionScript 3.
Get It!
- strnatcmp.c,strnatcmp.h- the algorithm itself
- natsort.c- example driver program. (Tryls -F /proc | natsort)
- textutils.diff- patch to add natural sort to sort(1) from GNU textutils-2.0; use the new-Noption.
- Natural ordering is now in PHP4rc2, through thestrnatcasecmpandstrnatcmpfunctions.
To Do
Comparison of characters is purely numeric, without taking character set or locale into account. So it is only correct for ASCII. This should probably be a separate function because doing the comparisons will probably introduce a dependency on the OS mechanism for finding the locale and comparing characters.
It might be good to support multibyte character sets too.
If you fix either of these, please mail me. They should not be very hard.