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Text::Soundex - Implementation of the Soundex Algorithm as Described by Knuth |
Text::Soundex - Implementation of the Soundex Algorithm as Described by Knuth
use Text::Soundex 'soundex';
$code = soundex($name); # Get the soundex code for a name. @codes = soundex(@names); # Get the list of codes for a list of names.
# Redefine the value that soundex() will return if the input string # contains no identifiable sounds within it. $Text::Soundex::nocode = 'Z000';
This module implements the soundex algorithm as described by Donald Knuth in Volume 3 of The Art of Computer Programming. The algorithm is intended to hash words (in particular surnames) into a small space using a simple model which approximates the sound of the word when spoken by an English speaker. Each word is reduced to a four character string, the first character being an upper case letter and the remaining three being digits.
The value returned for strings which have no soundex encoding is
defined using $Text::Soundex::nocode. The default value is undef,
however values such as 'Z000' are commonly used alternatives.
For backward compatibility with older versions of this module the
$Text::Soundex::nocode is exported into the caller's namespace as
$soundex_nocode.
In scalar context, soundex() returns the soundex code of its first
argument. In list context, a list is returned in which each element is the
soundex code for the corresponding argument passed to soundex(). For
example, the following code assigns @codes the value ('M200', 'S320'):
@codes = soundex qw(Mike Stok);
To use Text::Soundex to generate codes that can be used to search one
of the publically available US Censuses, a variant of the soundex()
subroutine must be used:
use Text::Soundex 'soundex_nara';
$code = soundex_nara($name);
The algorithm used by the US Censuses is slightly different than that defined by Knuth and others. The descrepancy shows up in names such as ``Ashcraft'':
use Text::Soundex qw(soundex soundex_nara);
print soundex("Ashcraft"), "\n"; # prints: A226
print soundex_nara("Ashcraft"), "\n"; # prints: A261
Knuth's examples of various names and the soundex codes they map to are listed below:
Euler, Ellery -> E460 Gauss, Ghosh -> G200 Hilbert, Heilbronn -> H416 Knuth, Kant -> K530 Lloyd, Ladd -> L300 Lukasiewicz, Lissajous -> L222
so:
$code = soundex 'Knuth'; # $code contains 'K530' @list = soundex qw(Lloyd Gauss); # @list contains 'L300', 'G200'
As the soundex algorithm was originally used a long time ago in the US it considers only the English alphabet and pronunciation. In particular, non-ASCII characters will be ignored. The recommended method of dealing with characters that have accents, or other unicode characters, is to use the Text::Unidecode module available from CPAN. Either use the module explicitly:
use Text::Soundex;
use Text::Unidecode;
print soundex(unidecode("Fran\xE7ais")), "\n"; # Prints "F652\n"
Or use the convenient wrapper routine:
use Text::Soundex 'soundex_unicode';
print soundex_unicode("Fran\xE7ais"), "\n"; # Prints "F652\n"
Since the soundex algorithm maps a large space (strings of arbitrary
length) onto a small space (single letter plus 3 digits) no inference
can be made about the similarity of two strings which end up with the
same soundex code. For example, both Hilbert and Heilbronn end
up with a soundex code of H416.
This module is currently maintain by Mark Mielke (mark@mielke.cc).
Version 3 is a significant update to provide support for versions of
Perl later than Perl 5.004. Specifically, the XS version of the
soundex() subroutine understands strings that are encoded using UTF-8
(unicode strings).
Version 2 of this module was a re-write by Mark Mielke (mark@mielke.cc)
to improve the speed of the subroutines. The XS version of the soundex()
subroutine was introduced in 2.00.
Version 1 of this module was written by Mike Stok (mike@stok.co.uk)
and was included into the Perl core library set.
Dave Carlsen (dcarlsen@csranet.com) made the request for the NARA
algorithm to be included. The NARA soundex page can be viewed at:
http://www.nara.gov/genealogy/soundex/soundex.html
Ian Phillips (ian@pipex.net) and Rich Pinder (rpinder@hsc.usc.edu)
supplied ideas and spotted mistakes for v1.x.
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Text::Soundex - Implementation of the Soundex Algorithm as Described by Knuth |