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Better plural stemmer than minimal_english (#4738)
Drops the trailing "e" in taxes, dresses, watches, dishes etc that otherwise cause mismatches with plural and singular forms. Signed-off-by: Nicholas Walter Knize <[email protected]> Co-authored-by: Mark Harwood <[email protected]> Co-authored-by: Nicholas Walter Knize <[email protected]> (cherry picked from commit c92846d)
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...analysis-common/src/main/java/org/opensearch/analysis/common/EnglishPluralStemFilter.java
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| /* | ||
| * SPDX-License-Identifier: Apache-2.0 | ||
| * | ||
| * The OpenSearch Contributors require contributions made to | ||
| * this file be licensed under the Apache-2.0 license or a | ||
| * compatible open source license. | ||
| */ | ||
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| /* | ||
| * Licensed to Elasticsearch under one or more contributor | ||
| * license agreements. See the NOTICE file distributed with | ||
| * this work for additional information regarding copyright | ||
| * ownership. Elasticsearch licenses this file to you under | ||
| * the Apache License, Version 2.0 (the "License"); you may | ||
| * not use this file except in compliance with the License. | ||
| * You may obtain a copy of the License at | ||
| * | ||
| * http://www.apache.org/licenses/LICENSE-2.0 | ||
| * | ||
| * Unless required by applicable law or agreed to in writing, | ||
| * software distributed under the License is distributed on an | ||
| * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY | ||
| * KIND, either express or implied. See the License for the | ||
| * specific language governing permissions and limitations | ||
| * under the License. | ||
| */ | ||
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| /* | ||
| * Modifications Copyright OpenSearch Contributors. See | ||
| * GitHub history for details. | ||
| */ | ||
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| package org.opensearch.analysis.common; | ||
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| import org.apache.lucene.analysis.TokenFilter; | ||
| import org.apache.lucene.analysis.TokenStream; | ||
| import org.apache.lucene.analysis.en.EnglishMinimalStemFilter; | ||
| import org.apache.lucene.analysis.tokenattributes.CharTermAttribute; | ||
| import org.apache.lucene.analysis.tokenattributes.KeywordAttribute; | ||
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| import java.io.IOException; | ||
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| public final class EnglishPluralStemFilter extends TokenFilter { | ||
| private final EnglishPluralStemmer stemmer = new EnglishPluralStemmer(); | ||
| private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class); | ||
| private final KeywordAttribute keywordAttr = addAttribute(KeywordAttribute.class); | ||
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| public EnglishPluralStemFilter(TokenStream input) { | ||
| super(input); | ||
| } | ||
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| @Override | ||
| public boolean incrementToken() throws IOException { | ||
| if (input.incrementToken()) { | ||
| if (!keywordAttr.isKeyword()) { | ||
| final int newlen = stemmer.stem(termAtt.buffer(), termAtt.length()); | ||
| termAtt.setLength(newlen); | ||
| } | ||
| return true; | ||
| } else { | ||
| return false; | ||
| } | ||
| } | ||
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| /** | ||
| * Plural stemmer for English based on the {@link EnglishMinimalStemFilter} | ||
| * <p> | ||
| * This stemmer removes plurals but beyond EnglishMinimalStemFilter adds | ||
| * four new suffix rules to remove dangling e characters: | ||
| * <ul> | ||
| * <li>xes - "boxes" becomes "box"</li> | ||
| * <li>sses - "dresses" becomes "dress"</li> | ||
| * <li>shes - "dishes" becomes "dish"</li> | ||
| * <li>tches - "watches" becomes "watch"</li> | ||
| * </ul> | ||
| * See https://github.com/elastic/elasticsearch/issues/42892 | ||
| * <p> | ||
| * In addition the s stemmer logic is amended so that | ||
| * <ul> | ||
| * <li>ees->ee so that bees matches bee</li> | ||
| * <li>ies->y only on longer words to that ties matches tie</li> | ||
| * <li>oes->o rule so that tomatoes matches tomato but retains e for some words eg shoes to shoe</li> | ||
| * </ul> | ||
| */ | ||
| public static class EnglishPluralStemmer { | ||
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| // Words ending in oes that retain the e when stemmed | ||
| public static final char[][] oesExceptions = { "shoes".toCharArray(), "canoes".toCharArray(), "oboes".toCharArray() }; | ||
| // Words ending in ches that retain the e when stemmed | ||
| public static final char[][] chesExceptions = { | ||
| "cliches".toCharArray(), | ||
| "avalanches".toCharArray(), | ||
| "mustaches".toCharArray(), | ||
| "moustaches".toCharArray(), | ||
| "quiches".toCharArray(), | ||
| "headaches".toCharArray(), | ||
| "heartaches".toCharArray(), | ||
| "porsches".toCharArray(), | ||
| "tranches".toCharArray(), | ||
| "caches".toCharArray() }; | ||
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| @SuppressWarnings("fallthrough") | ||
| public int stem(char s[], int len) { | ||
| if (len < 3 || s[len - 1] != 's') return len; | ||
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| switch (s[len - 2]) { | ||
| case 'u': | ||
| case 's': | ||
| return len; | ||
| case 'e': | ||
| // Modified ies->y logic from original s-stemmer - only work on strings > 4 | ||
| // so spies -> spy still but pies->pie. | ||
| // The original code also special-cased aies and eies for no good reason as far as I can tell. | ||
| // ( no words of consequence - eg http://www.thefreedictionary.com/words-that-end-in-aies ) | ||
| if (len > 4 && s[len - 3] == 'i') { | ||
| s[len - 3] = 'y'; | ||
| return len - 2; | ||
| } | ||
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| // Suffix rules to remove any dangling "e" | ||
| if (len > 3) { | ||
| // xes (but >1 prefix so we can stem "boxes->box" but keep "axes->axe") | ||
| if (len > 4 && s[len - 3] == 'x') { | ||
| return len - 2; | ||
| } | ||
| // oes | ||
| if (len > 3 && s[len - 3] == 'o') { | ||
| if (isException(s, len, oesExceptions)) { | ||
| // Only remove the S | ||
| return len - 1; | ||
| } | ||
| // Remove the es | ||
| return len - 2; | ||
| } | ||
| if (len > 4) { | ||
| // shes/sses | ||
| if (s[len - 4] == 's' && (s[len - 3] == 'h' || s[len - 3] == 's')) { | ||
| return len - 2; | ||
| } | ||
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| // ches | ||
| if (len > 4) { | ||
| if (s[len - 4] == 'c' && s[len - 3] == 'h') { | ||
| if (isException(s, len, chesExceptions)) { | ||
| // Only remove the S | ||
| return len - 1; | ||
| } | ||
| // Remove the es | ||
| return len - 2; | ||
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| } | ||
| } | ||
| } | ||
| } | ||
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| default: | ||
| return len - 1; | ||
| } | ||
| } | ||
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| private boolean isException(char[] s, int len, char[][] exceptionsList) { | ||
| for (char[] oesRule : exceptionsList) { | ||
| int rulePos = oesRule.length - 1; | ||
| int sPos = len - 1; | ||
| boolean matched = true; | ||
| while (rulePos >= 0 && sPos >= 0) { | ||
| if (oesRule[rulePos] != s[sPos]) { | ||
| matched = false; | ||
| break; | ||
| } | ||
| rulePos--; | ||
| sPos--; | ||
| } | ||
| if (matched) { | ||
| return true; | ||
| } | ||
| } | ||
| return false; | ||
| } | ||
| } | ||
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| } |
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