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1 ;;; soundex.el -- implement Soundex algorithm
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2
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3 ;; Copyright (C) 1993 Free Software Foundation, Inc.
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4
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5 ;; Author: Christian Plaunt <chris@bliss.berkeley.edu>
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6 ;; Maintainer: FSF
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7 ;; Keywords: matching
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8 ;; Created: Sat May 15 14:48:18 1993
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9
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10 ;; This file is part of GNU Emacs.
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11
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12 ;; GNU Emacs is free software; you can redistribute it and/or modify
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13 ;; it under the terms of the GNU General Public License as published by
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14 ;; the Free Software Foundation; either version 2, or (at your option)
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15 ;; any later version.
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16
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17 ;; GNU Emacs is distributed in the hope that it will be useful,
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18 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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19 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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20 ;; GNU General Public License for more details.
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21
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22 ;; You should have received a copy of the GNU General Public License
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23 ;; along with GNU Emacs; see the file COPYING. If not, write to
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24 ;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
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25
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26 ;;; Synched up with: FSF 19.30.
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27
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28 ;;; Commentary:
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29
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30 ;; The Soundex algorithm maps English words into representations of
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31 ;; how they sound. Words with vaguely similar sound map to the same string.
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32
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33 ;;; Code:
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34
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35 (defvar soundex-alist
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36 '((?B . "1") (?F . "1") (?P . "1") (?V . "1")
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37 (?C . "2") (?G . "2") (?J . "2") (?K . "2") (?Q . "2") (?S . "2")
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38 (?X . "2") (?Z . "2") (?D . "3") (?T . "3") (?L . "4") (?M . "5")
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39 (?N . "5") (?R . "6"))
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40 "Alist of chars-to-key-code for building Soundex keys.")
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41
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42 (defun soundex (word)
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43 "Return a Soundex key for WORD.
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44 Implemented as described in:
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45 Knuth, Donald E. \"The Art of Computer Programming, Vol. 3: Sorting
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46 and Searching\", Addison-Wesley (1973), pp. 391-392."
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47 (let* ((word (upcase word)) (length (length word))
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48 (code (cdr (assq (aref word 0) soundex-alist)))
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49 (key (substring word 0 1)) (index 1) (prev-code code))
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50 ;; once we have a four char key, we're done
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51 (while (and (> 4 (length key)) (< index length))
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52 ;; look up the code for each letter in word at index
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53 (setq code (cdr (assq (aref word index) soundex-alist))
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54 index (1+ index)
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55 ;; append code to key unless the same codes belong to
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56 ;; adjacent letters in the original string
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57 key (concat key (if (or (null code) (string= code prev-code))
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58 ()
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59 code))
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60 prev-code code))
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61 ;; return a key that is 4 chars long and padded by "0"s if needed
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62 (if (> 4 (length key))
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63 (substring (concat key "000") 0 4)
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64 key)))
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65
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66 ;(defvar soundex-test
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67 ; '("Euler" "Gauss" "Hilbert" "Knuth" "Lloyd" "Lukasiewicz"
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68 ; "Ellery" "Ghosh" "Heilbronn" "Kant" "Ladd" "Lissajous")
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69 ; "\n Knuth's names to demonstrate the Soundex algorithm.")
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70 ;
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71 ;(mapcar 'soundex soundex-test)
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72 ;("E460" "G200" "H416" "K530" "L300" "L222"
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73 ; "E460" "G200" "H416" "K530" "L300" "L222")
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74
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75 ;; soundex.el ends here
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