code: /* LanguageTool, a natural language style checker 
   * Copyright (C) 2015 Daniel Naber (http://www.danielnaber.de)
   * 
   * This library is free software; you can redistribute it and/or
   * modify it under the terms of the GNU Lesser General Public
   * License as published by the Free Software Foundation; either
   * version 2.1 of the License, or (at your option) any later version.
   *
   * This library is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * Lesser General Public License for more details.
   *
   * You should have received a copy of the GNU Lesser General Public
   * License along with this library; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301
   * USA
   */
  package org.languagetool.languagemodel;
  
  import org.languagetool.rules.ngrams.Probability;
  
  import java.util.List;
  
  /**
   * Combines the results of several {@link LanguageModel}s.
   * @since 3.2
   */
  public class MultiLanguageModel implements LanguageModel {
  
    private final List<LanguageModel> lms;
  
    public MultiLanguageModel(List<LanguageModel> lms) {
      if (lms.isEmpty()) {
        throw new IllegalArgumentException("List of language models is empty");
      }
      this.lms = lms;
    }
  
    @Override
    public Probability getPseudoProbability(List<String> context) {
      double prob = 0;
      float coverage = 0;
      long occurrences = 0;
      for (LanguageModel lm : lms) {
        Probability pProb = lm.getPseudoProbability(context);
        //System.out.println(i + ". " + pProb.getProb() + " (" + pProb.getCoverage() + ")");
        // TODO: decide what's the proper way to combine the probabilities
        prob += pProb.getProb();
        coverage += pProb.getCoverage();
        occurrences += pProb.getOccurrences();
      }
      return new Probability(prob, coverage/lms.size(), occurrences);
    }
  
    @Override
    public void close() {
      lms.stream().forEach(LanguageModel::close);
    }
  
    @Override
    public String toString() {
      return lms.toString();
    }
  }
  