Text::Soundex(3p)Perl Programmers Reference GuidText::Soundex(3p)
Text::Soundex - Implementation of the Soundex Algorithm as Described by Knuth
use Text::Soundex; $code = soundex $string; # get soundex code for a string @codes = soundex @list; # get list of codes for list of strings # set value to be returned for strings without soundex code $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 sur- names) into a small space using a simple model which approx- imates 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. If there is no soundex code representation for a string then the value of $soundex_nocode is returned. This is initially set to "undef", but many people seem to prefer an unlikely value like "Z000" (how unlikely this is depends on the data set being dealt with.) Any value can be assigned to $soundex_nocode. In scalar context "soundex" returns the soundex code of its first argument, and in list context a list is returned in which each element is the soundex code for the corresponding argument passed to "soundex" e.g. @codes = soundex qw(Mike Stok); leaves @codes containing "('M200', 'S320')".
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 perl v5.8.8 2005-02-05 1 Text::Soundex(3p)Perl Programmers Reference GuidText::Soundex(3p) 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 pronun- ciation. As it is mapping a large space (arbitrary length strings) onto a small space (single letter plus 3 digits) no infer- ence can be made about the similarity of two strings which end up with the same soundex code. For example, both "Hil- bert" and "Heilbronn" end up with a soundex code of "H416".
This code was implemented by Mike Stok ("firstname.lastname@example.org") from the description given by Knuth. Ian Phillipps ("email@example.com") and Rich Pinder ("firstname.lastname@example.org") supplied ideas and spotted mistakes. perl v5.8.8 2005-02-05 2
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