1 Introduction
2 Characters, Ordinals, and Codes
3 Hashing
soundex/ narahw/ start
4 Prefixing
soundex/ narahw
soundex-nara/ prefixing
soundex-old/ prefixing
soundex/ p
5 History
6 Legal
Version: 0.3

soundex: Soundex Index Keying in Scheme

Neil Van Dyke

License: LGPL 3   Web: http://www.neilvandyke.org/soundex-scheme/

 (require (planet neil/soundex:1:1))

1 Introduction

The soundex library provides an implementation in Scheme of the Soundex indexing hash function as specified somewhat loosely by US National Archives and Records Administration (NARA) publication [Soundex], and verified empirically against test cases from various sources. Both the current NARA function and the older version with different handling of `H’ and `W’ are supported.

Additionally, a nonstandard prefix-guessing function that is an invention of this lirbray function permits additional Soundex keys to be generated from a string, increasing recall.

This library should work under any R5RS Scheme implementation for which char->integer yields ASCII values.

2 Characters, Ordinals, and Codes

To facilitate possible future support of other input character sets, this library employs a character ordinal abstract representation of the letters used by Soundex. The ordinal value is an integer from 0 to 25 – corresponding to the 26 letters `A’ through `Z’, respectively – and can be used for fast mapping via vectors. Most applications need not be aware of this.

(soundex-ordinal chr)  any/c
  chr : any/c

Yields the Soundex ordinal value of character chr, of #f if the character is not considered a letter.

  (soundex-ordinal #\a) ==> 0
  (soundex-ordinal #\A) ==> 0
  (soundex-ordinal #\Z) ==> 25
  (soundex-ordinal #\3) ==> #f
  (soundex-ordinal #\.) ==> #f

(soundex-ordinal->char ord)  any/c
  ord : any/c

Yields the upper-case letter character that corresponds to the character ordinal value ord. For example:

  (soundex-ordinal->char (soundex-ordinal #\a)) ==> #\A

Note that an #f value as a result of applying soundex-ordinal is not an ordinal value, and is not mapped to a character by soundex-ordinal->char. For example:

  (soundex-ordinal->char (soundex-ordinal #\')) error-->

(soundex-ordinal->soundex-code ord)  any/c
  ord : any/c

Yields a library-specific Soundex code for character ordinal ord.

  (soundex-ordinal->soundex-code (soundex-ordinal #\a)) ==> aeiou
  (soundex-ordinal->soundex-code (soundex-ordinal #\c)) ==> #\2
  (soundex-ordinal->soundex-code (soundex-ordinal #\N)) ==> #\5
  (soundex-ordinal->soundex-code (soundex-ordinal #\w)) ==> hw
  (soundex-ordinal->soundex-code (soundex-ordinal #\y)) ==> y

(char->soundex-code chr)  any/c
  chr : any/c

Yields a library-specific Soundex code for character chr. This is equivalent to: (soundex-ordinal->soundex-code (soundex-ordinal chr)).

3 Hashing

Soundex hashes of strings can be generated with soundex-nara, soundex-old, and soundex.

(soundex/narahw/start str narahw? start)  any/c
  str : any/c
  narahw? : any/c
  start : any/c

This is an internal procedure.

  (soundex/narahw/start "van Dam" #t 4) ==> "D500"
  (soundex/narahw/start ".0,!"    #t 0) ==> #f

(soundex-nara str)  any/c
  str : any/c

(soundex-old str)  any/c
  str : any/c

(soundex str)  any/c
  str : any/c

Yields a Soundex hash key of string str, or #f if not even an initial letter could be found. soundex-nara generates NARA hashes, and soundex-old generates older-style hashes. soundex is an alias for soundex-nara.

  (soundex-nara "Ashcraft") ==> "A261"
  (soundex-old  "Ashcraft") ==> "A226"
  (soundex      "Ashcraft") ==> "A261"
  (soundex      "")         ==> #f

4 Prefixing

Multiple Soundex hashes from a single string can be generated by soundex-nara/prefixing, soundex-old/prefixing, and soundex/p, which consider the string with and without various common surname prefixes.

(soundex-prefix-starts str)  any/c
  str : any/c

Yields a list of Soundex start points in string str, as character index integers, for making hash keys with and without prefixes. A prefix must be followed by at least two letters, although they can be interspersed with non-letter characters. The exact behavior of this function is subject to change in future versions of this library.

  (soundex-prefix-starts "Smith")          ==> (0)
  (soundex-prefix-starts "  Jones")        ==> (2)
  (soundex-prefix-starts "vanderlinden")   ==> (0 3 6)
  (soundex-prefix-starts "van der linden") ==> (0 3 7)
  (soundex-prefix-starts "")               ==> ()
  (soundex-prefix-starts "123")            ==> ()
  (soundex-prefix-starts "dea")            ==> (0)
  (soundex-prefix-starts "dea ")           ==> (0)
  (soundex-prefix-starts "dean")           ==> (0)
  (soundex-prefix-starts "delasol")        ==> (0 2 3 4)

(soundex/narahw str narahw?)  any/c
  str : any/c
  narahw? : any/c

This is an internal procedure.

(soundex-nara/prefixing str)  any/c
  str : any/c

(soundex-old/prefixing str)  any/c
  str : any/c

(soundex/p str)  any/c
  str : any/c

Yields a list of zero or more Soundex hash keys from string str, based on the whole string and the string with various prefixes skipped. All elements of the list are mutually unique. soundex-nara/prefixing generates NARA hashes, and soundex-old/prefixing generates older-style hashes. soundex/p is an alias for soundex-nara/prefixing.

  (soundex/p "Van Damme") ==> ("V535" "D500")
  (soundex/p "vanvoom")   ==> ("V515" "V500")
  (soundex/p "vanvanvan") ==> ("V515")
  (soundex/p "DeLaSol")   ==> ("D424" "L240" "A240" "S400")
  (soundex/p "")          ==> ()

5 History

6 Legal

Copyright (c) 2004–2009 Neil Van Dyke. This program is Free Software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 3 of the License (LGPL 3), or (at your option) any later version. This program is distributed in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose. See http://www.gnu.org/licenses/ for details. For other licenses and consulting, please contact the author.