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comparison lisp/utils/soundex.el @ 0:376386a54a3c r19-14

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date Mon, 13 Aug 2007 08:45:50 +0200
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1 ;;; soundex.el -- implement Soundex algorithm
2
3 ;; Copyright (C) 1993 Free Software Foundation, Inc.
4
5 ;; Author: Christian Plaunt <chris@bliss.berkeley.edu>
6 ;; Maintainer: FSF
7 ;; Keywords: matching
8 ;; Created: Sat May 15 14:48:18 1993
9
10 ;; This file is part of GNU Emacs.
11
12 ;; GNU Emacs is free software; you can redistribute it and/or modify
13 ;; it under the terms of the GNU General Public License as published by
14 ;; the Free Software Foundation; either version 2, or (at your option)
15 ;; any later version.
16
17 ;; GNU Emacs is distributed in the hope that it will be useful,
18 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
19 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 ;; GNU General Public License for more details.
21
22 ;; You should have received a copy of the GNU General Public License
23 ;; along with GNU Emacs; see the file COPYING. If not, write to
24 ;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
25
26 ;;; Synched up with: FSF 19.30.
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.
44 Implemented as described in:
45 Knuth, Donald E. \"The Art of Computer Programming, Vol. 3: Sorting
46 and 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 ;; soundex.el ends here