Java tutorial
/******************************************************************************* * Copyright 2013 * Ubiquitous Knowledge Processing (UKP) Lab * Technische Universitt Darmstadt * * Licensed 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. ******************************************************************************/ package de.tudarmstadt.ukp.dkpro.core.langdect; import static de.tudarmstadt.ukp.dkpro.core.frequency.Web1TProviderBase.BOS; import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; import org.apache.commons.lang.StringUtils; import org.apache.uima.UimaContext; import org.apache.uima.analysis_engine.AnalysisEngineProcessException; import org.apache.uima.fit.component.JCasAnnotator_ImplBase; import org.apache.uima.fit.descriptor.ConfigurationParameter; import org.apache.uima.fit.descriptor.ExternalResource; import org.apache.uima.fit.util.JCasUtil; import org.apache.uima.jcas.JCas; import org.apache.uima.resource.ResourceInitializationException; import de.tudarmstadt.ukp.dkpro.core.api.frequency.provider.FrequencyCountProvider; import de.tudarmstadt.ukp.dkpro.core.api.frequency.util.FrequencyUtils; import de.tudarmstadt.ukp.dkpro.core.api.segmentation.type.Token; import de.tudarmstadt.ukp.dkpro.core.ngrams.util.NGramStringIterable; /** * Language detector based on n-gram frequency counts, e.g. as provided by Web1T * * @author zesch * */ public class LanguageDetector extends JCasAnnotator_ImplBase { /** * An array of external resources of frequency providers (one for each language that should be detected). */ public static final String PARAM_FREQUENCY_PROVIDER_RESOURCES = "frequencyProviders"; @ExternalResource(key = PARAM_FREQUENCY_PROVIDER_RESOURCES, mandatory = true) private FrequencyCountProvider[] frequencyProviders; /** * The minimum n-gram size that should be considered. Default is 1. */ public static final String PARAM_MIN_NGRAM_SIZE = "minNGramSize"; @ConfigurationParameter(name = PARAM_MIN_NGRAM_SIZE, mandatory = true, defaultValue = "1") private int minNGramSize; /** * The maximum n-gram size that should be considered. Default is 3. */ public static final String PARAM_MAX_NGRAM_SIZE = "maxNGramSize"; @ConfigurationParameter(name = PARAM_MAX_NGRAM_SIZE, mandatory = true, defaultValue = "3") private int maxNGramSize; private Map<String, FrequencyCountProvider> providerMap; @Override public void initialize(UimaContext context) throws ResourceInitializationException { super.initialize(context); providerMap = new HashMap<String, FrequencyCountProvider>(); for (FrequencyCountProvider provider : frequencyProviders) { try { providerMap.put(provider.getLanguage(), provider); } catch (Exception e) { throw new ResourceInitializationException(e); } } } @Override public void process(JCas jcas) throws AnalysisEngineProcessException { List<String> words = JCasUtil.toText(JCasUtil.select(jcas, Token.class)); if (words.size() < 1) { return; } List<String> ngrams = new ArrayList<String>(); if (words.size() > 1) { ngrams.add(getNgram(BOS, words.get(0), words.get(1))); } for (String ngram : new NGramStringIterable(words, 1, 3)) { ngrams.add(ngram); } try { Map<String, Double> langProbs = getLanguageProbabilities(ngrams); String maxLanguage = "x-unspecified"; double maxLogProb = Double.NEGATIVE_INFINITY; for (String lang : langProbs.keySet()) { double prob = langProbs.get(lang); if (prob > maxLogProb) { maxLogProb = prob; maxLanguage = lang; } System.out.println(lang + " - " + prob); } jcas.setDocumentLanguage(maxLanguage); } catch (Exception e) { throw new AnalysisEngineProcessException(e); } } private Map<String, Double> getLanguageProbabilities(List<String> ngrams) throws Exception { Map<String, Double> langProbs = new HashMap<String, Double>(); for (String lang : providerMap.keySet()) { FrequencyCountProvider provider = providerMap.get(lang); long nrOfUnigrams = provider.getNrOfNgrams(1); long nrOfBigrams = provider.getNrOfNgrams(2); long nrOfTrigrams = provider.getNrOfNgrams(3); double textLogProbability = 0.0; for (String ngram : ngrams) { long frequency = provider.getFrequency(ngram); int ngramSize = FrequencyUtils.getPhraseLength(ngram); long normalization = 1; int weighting = 1; if (ngramSize == 1) { normalization = nrOfUnigrams; } else if (ngramSize == 2) { weighting = 2; normalization = nrOfBigrams; } else if (ngramSize == 3) { weighting = 4; normalization = nrOfTrigrams; } if (frequency > 0) { double logProb = Math.log(weighting * ((double) frequency) / normalization); textLogProbability += logProb; } else { textLogProbability += Math.log(1.0 / normalization); } } langProbs.put(lang, textLogProbability); } return langProbs; } private String getNgram(String... strings) { return StringUtils.join(strings, " "); } }