001/**
002 * Copyright (c) 2011, The University of Southampton and the individual contributors.
003 * All rights reserved.
004 *
005 * Redistribution and use in source and binary forms, with or without modification,
006 * are permitted provided that the following conditions are met:
007 *
008 *   *  Redistributions of source code must retain the above copyright notice,
009 *      this list of conditions and the following disclaimer.
010 *
011 *   *  Redistributions in binary form must reproduce the above copyright notice,
012 *      this list of conditions and the following disclaimer in the documentation
013 *      and/or other materials provided with the distribution.
014 *
015 *   *  Neither the name of the University of Southampton nor the names of its
016 *      contributors may be used to endorse or promote products derived from this
017 *      software without specific prior written permission.
018 *
019 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
020 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
021 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
022 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
023 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
024 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
025 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
026 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
027 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
028 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
029 */
030package org.openimaj.text.nlp.namedentity;
031
032import java.lang.reflect.Array;
033import java.util.ArrayList;
034import java.util.List;
035
036import org.apache.commons.lang.StringUtils;
037
038/**
039 * Utility class which allows generation of N-grams of items in a list. Ngrams
040 * are defined as "n" neighbouring items
041 * 
042 * @author Laurence Willmore (lgw1e10@ecs.soton.ac.uk)
043 * @author Sina Samangooei (ss@ecs.soton.ac.uk)
044 * 
045 * @param <T>
046 */
047public class NGramGenerator<T> {
048
049        /**
050         * Produce n-grams of strings
051         * 
052         * @author Laurence Willmore (lgw1e10@ecs.soton.ac.uk)
053         * @author Sina Samangooei (ss@ecs.soton.ac.uk)
054         * 
055         */
056        public static class StringNGramGenerator extends NGramGenerator<String> {
057
058                /**
059                 * Class {@link NGramGenerator#NGramGenerator(Class)} with String#class
060                 */
061                public StringNGramGenerator() {
062                        super(String.class);
063                }
064
065        }
066
067        private final Class<T> clazz;
068
069        /**
070         * @param type
071         *            provide the type of the items in the list being generated
072         */
073        public NGramGenerator(Class<T> type) {
074                clazz = type;
075        }
076
077        /**
078         * @param tokens
079         *            tokens to combine as ngrams
080         * @param ngrams
081         *            the numbers of ngrams to generat
082         * @return a list of ngrams
083         */
084        @SuppressWarnings("unchecked")
085        public <R extends T> List<T[]> getNGrams(List<R> tokens, int... ngrams) {
086                if (tokens == null)
087                        return new ArrayList<T[]>();
088                final ArrayList<T[]> result = new ArrayList<T[]>();
089                for (int i = 0; i < tokens.size(); i++) {
090                        for (final int nsize : ngrams) {
091                                if (i + nsize <= tokens.size()) {
092                                        final R[] ngram = (R[]) Array.newInstance(clazz, nsize);
093                                        for (int j = 0; j < nsize; j++) {
094                                                ngram[j] = tokens.get(i + j);
095                                        }
096                                        result.add(ngram);
097                                }
098                        }
099                }
100                return result;
101        }
102
103        /**
104         * lightweight test with some really horrible unicode
105         * 
106         * @param args
107         */
108        public static void main(String[] args) {
109                // final ArrayList<String> tokens = new
110                // ArrayList<String>(Arrays.asList(tokA));
111                final NGramGenerator<String> ngg = new StringNGramGenerator();
112
113                final List<String[]> ngrams = ngg.getNGrams(null, 3);
114                for (final String[] ngram : ngrams) {
115                        System.out.println(StringUtils.join(ngram, " "));
116                }
117        }
118
119}