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66 lines
2.4 KiB
EmacsLisp
66 lines
2.4 KiB
EmacsLisp
;;; soundex.el --- implement Soundex algorithm -*- lexical-binding: t -*-
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;; Copyright (C) 1993, 2001-2021 Free Software Foundation, Inc.
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;; Author: Christian Plaunt <chris@bliss.berkeley.edu>
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;; Maintainer: emacs-devel@gnu.org
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;; Keywords: matching
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;; Created: Sat May 15 14:48:18 1993
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;; This file is part of GNU Emacs.
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;; GNU Emacs is free software: you can redistribute it and/or modify
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;; it under the terms of the GNU General Public License as published by
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;; the Free Software Foundation, either version 3 of the License, or
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;; (at your option) any later version.
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;; GNU Emacs is distributed in the hope that it will be useful,
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;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;; GNU General Public License for more details.
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;; You should have received a copy of the GNU General Public License
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;; along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>.
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;;; Commentary:
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;; The Soundex algorithm maps English words into representations of
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;; how they sound. Words with vaguely similar sound map to the same string.
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;;; Code:
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(defconst soundex-alist
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'((?B . "1") (?F . "1") (?P . "1") (?V . "1")
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(?C . "2") (?G . "2") (?J . "2") (?K . "2") (?Q . "2") (?S . "2")
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(?X . "2") (?Z . "2") (?D . "3") (?T . "3") (?L . "4") (?M . "5")
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(?N . "5") (?R . "6"))
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"Alist of chars-to-key-code for building Soundex keys.")
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(defun soundex (word)
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"Return a Soundex key for WORD.
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Implemented as described in:
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Knuth, Donald E. \"The Art of Computer Programming, Vol. 3: Sorting
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and Searching\", Addison-Wesley (1973), pp. 391-392."
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(let* ((word (upcase word)) (length (length word))
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(code (cdr (assq (aref word 0) soundex-alist)))
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(key (substring word 0 1)) (index 1) (prev-code code))
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;; once we have a four char key, we're done
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(while (and (> 4 (length key)) (< index length))
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;; look up the code for each letter in word at index
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(setq code (cdr (assq (aref word index) soundex-alist))
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index (1+ index)
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;; append code to key unless the same codes belong to
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;; adjacent letters in the original string
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key (concat key (if (or (null code) (string= code prev-code))
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()
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code))
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prev-code code))
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;; return a key that is 4 chars long and padded by "0"s if needed
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(if (> 4 (length key))
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(substring (concat key "000") 0 4)
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key)))
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(provide 'soundex)
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;;; soundex.el ends here
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