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Merge pull request #61 from gmarty/transliterator-ja
Japanese transliterator (Hiragana and Katakana) to Latin
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| /* | ||
| Copyright (c) 2012, Guillaume Marty | ||
| Permission is hereby granted, free of charge, to any person obtaining a copy | ||
| of this software and associated documentation files (the "Software"), to deal | ||
| in the Software without restriction, including without limitation the rights | ||
| to use, copy, modify, merge, publish, distribute, sublicense, and/or sell | ||
| copies of the Software, and to permit persons to whom the Software is | ||
| furnished to do so, subject to the following conditions: | ||
| The above copyright notice and this permission notice shall be included in | ||
| all copies or substantial portions of the Software. | ||
| THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR | ||
| IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, | ||
| FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE | ||
| AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER | ||
| LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, | ||
| OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN | ||
| THE SOFTWARE. | ||
| */ | ||
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| /** | ||
| * A very basic stemmer that performs the following steps: | ||
| * * Stem katakana. | ||
| * Inspired by: | ||
| * http://svn.apache.org/repos/asf/lucene/dev/trunk/lucene/analysis/kuromoji/src/java/org/apache/lucene/analysis/ja/JapaneseKatakanaStemFilter.java | ||
| * | ||
| * \@todo Use .bind() in StemmerJa.prototype.attach(). | ||
| */ | ||
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| var Tokenizer = require('../tokenizers/tokenizer_ja'); | ||
| var stopwords = require('../util/stopwords_ja'); | ||
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| /** | ||
| * @constructor | ||
| */ | ||
| var StemmerJa = function() { | ||
| }; | ||
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| /** | ||
| * Tokenize and stem a text. | ||
| * Stop words are excluded except if the second argument is true. | ||
| * | ||
| * @param {string} text | ||
| * @param {boolean} keepStops Whether to keep stop words from the output or not. | ||
| * @return {Array.<string>} | ||
| */ | ||
| StemmerJa.prototype.tokenizeAndStem = function(text, keepStops) { | ||
| var self = this; | ||
| var stemmedTokens = []; | ||
| var tokens = new Tokenizer().tokenize(text); | ||
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| // This is probably faster than an if at each iteration. | ||
| if (keepStops) { | ||
| tokens.forEach(function(token) { | ||
| var resultToken = token.toLowerCase(); | ||
| resultToken = self.stem(resultToken); | ||
| stemmedTokens.push(resultToken); | ||
| }); | ||
| } else { | ||
| tokens.forEach(function(token) { | ||
| if (stopwords.indexOf(token) == -1) { | ||
| var resultToken = token.toLowerCase(); | ||
| resultToken = self.stem(resultToken); | ||
| stemmedTokens.push(resultToken); | ||
| } | ||
| }); | ||
| } | ||
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| return stemmedTokens; | ||
| }; | ||
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| /** | ||
| * Stem a term. | ||
| * | ||
| * @param {string} token | ||
| * @return {string} | ||
| */ | ||
| StemmerJa.prototype.stem = function(token) { | ||
| token = this.stemKatakana(token); | ||
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| return token; | ||
| }; | ||
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| /** | ||
| * Remove the final prolonged sound mark on katakana if length is superior to | ||
| * a threshold. | ||
| * | ||
| * @param {string} token A katakana string to stem. | ||
| * @return {string} A katakana string stemmed. | ||
| */ | ||
| StemmerJa.prototype.stemKatakana = function(token) { | ||
| var HIRAGANA_KATAKANA_PROLONGED_SOUND_MARK = 'ー'; | ||
| var DEFAULT_MINIMUM_LENGTH = 4; | ||
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| if (token.length >= DEFAULT_MINIMUM_LENGTH | ||
| && token.slice(-1) === HIRAGANA_KATAKANA_PROLONGED_SOUND_MARK | ||
| && this.isKatakana(token)) { | ||
| token = token.slice(0, token.length - 1); | ||
| } | ||
| return token; | ||
| }; | ||
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| /** | ||
| * Is a string made of fullwidth katakana only? | ||
| * This implementation is the fastest I know: | ||
| * http://jsperf.com/string-contain-katakana-only/2 | ||
| * | ||
| * @param {string} str A string. | ||
| * @return {boolean} True if the string has katakana only. | ||
| */ | ||
| StemmerJa.prototype.isKatakana = function(str) { | ||
| return !!str.match(/^[ァ-ヴー]+$/); | ||
| }; | ||
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| // Expose an attach function that will patch String with new methods. | ||
| StemmerJa.prototype.attach = function() { | ||
| var self = this; | ||
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| String.prototype.stem = function() { | ||
| return self.stem(this); | ||
| }; | ||
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| String.prototype.tokenizeAndStem = function(keepStops) { | ||
| return self.tokenizeAndStem(this, keepStops); | ||
| }; | ||
| }; | ||
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| module.exports = StemmerJa; |
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