1;;; soundex.el --- implement Soundex algorithm
2
3;; Copyright (C) 1993, 2001, 2002, 2003, 2004, 2005,
4;;   2006, 2007 Free Software Foundation, Inc.
5
6;; Author: Christian Plaunt <chris@bliss.berkeley.edu>
7;; Maintainer: FSF
8;; Keywords: matching
9;; Created: Sat May 15 14:48:18 1993
10
11;; This file is part of GNU Emacs.
12
13;; GNU Emacs is free software; you can redistribute it and/or modify
14;; it under the terms of the GNU General Public License as published by
15;; the Free Software Foundation; either version 2, or (at your option)
16;; any later version.
17
18;; GNU Emacs is distributed in the hope that it will be useful,
19;; but WITHOUT ANY WARRANTY; without even the implied warranty of
20;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
21;; GNU General Public License for more details.
22
23;; You should have received a copy of the GNU General Public License
24;; along with GNU Emacs; see the file COPYING.  If not, write to the
25;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
26;; Boston, MA 02110-1301, USA.
27
28;;; Commentary:
29
30;; The Soundex algorithm maps English words into representations of
31;; how they sound.  Words with vaguely similar sound map to the same string.
32
33;;; Code:
34
35(defvar soundex-alist
36  '((?B . "1") (?F . "1") (?P . "1") (?V . "1")
37    (?C . "2") (?G . "2") (?J . "2") (?K . "2") (?Q . "2") (?S . "2")
38    (?X . "2") (?Z . "2") (?D . "3") (?T . "3") (?L . "4") (?M . "5")
39    (?N . "5") (?R . "6"))
40  "Alist of chars-to-key-code for building Soundex keys.")
41
42(defun soundex (word)
43  "Return a Soundex key for WORD.
44Implemented as described in:
45Knuth, Donald E. \"The Art of Computer Programming, Vol. 3: Sorting
46and Searching\", Addison-Wesley (1973), pp. 391-392."
47  (let* ((word (upcase word)) (length (length word))
48	 (code (cdr (assq (aref word 0) soundex-alist)))
49	 (key (substring word 0 1)) (index 1) (prev-code code))
50    ;; once we have a four char key, we're done
51    (while (and (> 4 (length key)) (< index length))
52      ;; look up the code for each letter in word at index
53      (setq code (cdr (assq (aref word index) soundex-alist))
54	    index (1+ index)
55	    ;; append code to key unless the same codes belong to
56	    ;; adjacent letters in the original string
57	    key (concat key (if (or (null code) (string= code prev-code))
58				()
59			      code))
60	    prev-code code))
61    ;; return a key that is 4 chars long and padded by "0"s if needed
62    (if (> 4 (length key))
63	(substring (concat key "000") 0 4)
64      key)))
65
66;(defvar soundex-test
67;  '("Euler" "Gauss" "Hilbert" "Knuth" "Lloyd" "Lukasiewicz"
68;    "Ellery" "Ghosh" "Heilbronn" "Kant" "Ladd" "Lissajous")
69;  "\n  Knuth's names to demonstrate the Soundex algorithm.")
70;
71;(mapcar 'soundex soundex-test)
72;("E460" "G200" "H416" "K530" "L300" "L222"
73; "E460" "G200" "H416" "K530" "L300" "L222")
74
75(provide 'soundex)
76
77;;; arch-tag: b2615a98-feb7-430e-a717-171086738953
78;;; soundex.el ends here
79