Text::Soundex - Implementation of the soundex algorithm.
- use Text::Soundex;
- # Original algorithm.
- $code = soundex($name); # Get the soundex code for a name.
- @codes = soundex(@names); # Get the list of codes for a list of names.
- # American Soundex variant (NARA) - Used for US census data.
- $code = soundex_nara($name); # Get the soundex code for a name.
- @codes = soundex_nara(@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';
Soundex is a phonetic algorithm for indexing names by sound, as pronounced in English. The goal is for names with the same pronunciation to be encoded to the same representation so that they can be matched despite minor differences in spelling. Soundex is the most widely known of all phonetic algorithms and is often used (incorrectly) as a synonym for "phonetic algorithm". Improvements to Soundex are the basis for many modern phonetic algorithms. (Wikipedia, 2007)
This module implements the original soundex algorithm developed by Robert Russell and Margaret Odell, patented in 1918 and 1922, as well as a variation called "American Soundex" used for US census data, and current maintained by the National Archives and Records Administration (NARA).
The soundex algorithm may be recognized from Donald Knuth's The Art of Computer Programming. The algorithm described by Knuth is the NARA algorithm.
The value returned for strings which have no soundex encoding is
. The default value is
however values such as
are commonly used alternatives.
For backward compatibility with older versions of this module the
is exported into the caller's namespace as
In scalar context,
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
example, the following code assigns @codes the value
- @codes = soundex qw(Mike Stok);
to generate codes that can be used to search one
of the publically available US Censuses, a variant of the soundex
algorithm must be used:
- use Text::Soundex;
- $code = soundex_nara($name);
An example of where these algorithm differ follows:
Donald Knuth's examples of 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
- $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:
Or use the convenient wrapper routine:
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
up with a soundex code of
This module is currently maintain by Mark Mielke (
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 (
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 (
and was included into the Perl core library set.
Dave Carlsen (
) made the request for the NARA
algorithm to be included. The NARA soundex page can be viewed at:
Ian Phillips (
) and Rich Pinder (
supplied ideas and spotted mistakes for v1.x.