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1 ;;; soundex.el --- implement Soundex algorithm
3 ;; Copyright (C) 1993, 2001-2015 Free Software Foundation, Inc.
5 ;; Author: Christian Plaunt <chris@bliss.berkeley.edu>
6 ;; Maintainer: emacs-devel@gnu.org
7 ;; Keywords: matching
8 ;; Created: Sat May 15 14:48:18 1993
10 ;; This file is part of GNU Emacs.
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 3 of the License, or
15 ;; (at your option) any later version.
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.
22 ;; You should have received a copy of the GNU General Public License
23 ;; along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>.
25 ;;; Commentary:
27 ;; The Soundex algorithm maps English words into representations of
28 ;; how they sound. Words with vaguely similar sound map to the same string.
30 ;;; Code:
32 (defvar soundex-alist
33 '((?B . "1") (?F . "1") (?P . "1") (?V . "1")
34 (?C . "2") (?G . "2") (?J . "2") (?K . "2") (?Q . "2") (?S . "2")
35 (?X . "2") (?Z . "2") (?D . "3") (?T . "3") (?L . "4") (?M . "5")
36 (?N . "5") (?R . "6"))
37 "Alist of chars-to-key-code for building Soundex keys.")
39 (defun soundex (word)
40 "Return a Soundex key for WORD.
41 Implemented as described in:
42 Knuth, Donald E. \"The Art of Computer Programming, Vol. 3: Sorting
43 and Searching\", Addison-Wesley (1973), pp. 391-392."
44 (let* ((word (upcase word)) (length (length word))
45 (code (cdr (assq (aref word 0) soundex-alist)))
46 (key (substring word 0 1)) (index 1) (prev-code code))
47 ;; once we have a four char key, we're done
48 (while (and (> 4 (length key)) (< index length))
49 ;; look up the code for each letter in word at index
50 (setq code (cdr (assq (aref word index) soundex-alist))
51 index (1+ index)
52 ;; append code to key unless the same codes belong to
53 ;; adjacent letters in the original string
54 key (concat key (if (or (null code) (string= code prev-code))
56 code))
57 prev-code code))
58 ;; return a key that is 4 chars long and padded by "0"s if needed
59 (if (> 4 (length key))
60 (substring (concat key "000") 0 4)
61 key)))
63 ;(defvar soundex-test
64 ; '("Euler" "Gauss" "Hilbert" "Knuth" "Lloyd" "Lukasiewicz"
65 ; "Ellery" "Ghosh" "Heilbronn" "Kant" "Ladd" "Lissajous")
66 ; "\n Knuth's names to demonstrate the Soundex algorithm.")
68 ;(mapcar 'soundex soundex-test)
69 ;("E460" "G200" "H416" "K530" "L300" "L222"
70 ; "E460" "G200" "H416" "K530" "L300" "L222")
72 (provide 'soundex)
74 ;;; soundex.el ends here