/*
* Carrot2 project.
*
* Copyright (C) 2002-2014, Dawid Weiss, Stanisław Osiński.
* All rights reserved.
*
* Refer to the full license file "carrot2.LICENSE"
* in the root folder of the repository checkout or at:
* http://www.carrot2.org/carrot2.LICENSE
*/
package org.carrot2.text.preprocessing;
import java.util.ArrayList;
import java.util.Set;
import org.carrot2.text.analysis.ITokenizer;
import org.carrot2.text.linguistic.IStemmer;
import org.carrot2.text.preprocessing.PreprocessingContext.AllStems;
import org.carrot2.text.preprocessing.PreprocessingContext.AllWords;
import org.carrot2.text.util.CharArrayComparators;
import org.carrot2.text.util.MutableCharArray;
import org.carrot2.util.CharArrayUtils;
import org.carrot2.util.attribute.Bindable;
import com.carrotsearch.hppc.ByteArrayList;
import com.carrotsearch.hppc.IntArrayList;
import com.carrotsearch.hppc.sorting.IndirectSort;
import com.google.common.collect.Lists;
import com.google.common.collect.Sets;
/**
* Applies stemming to words and calculates a number of frequency statistics for stems.
* <p>
* This class saves the following results to the {@link PreprocessingContext}:
* <ul>
* <li>{@link AllWords#stemIndex}</li>
* <li>{@link AllStems#image}</li>
* <li>{@link AllStems#mostFrequentOriginalWordIndex}</li>
* <li>{@link AllStems#tf}</li>
* <li>{@link AllStems#tfByDocument}</li>
* <li>{@link AllWords#type} is populated with {@link ITokenizer#TF_QUERY_WORD}</li>
* </ul>
*
* This class requires that {@link Tokenizer} and {@link CaseNormalizer} be invoked first.
*/
@Bindable(prefix = "LanguageModelStemmer")
public final class LanguageModelStemmer
{
/**
* Performs stemming and saves the results to the <code>context</code>.
*/
public void stem(PreprocessingContext context)
{
final IStemmer stemmer = context.language.getStemmer();
final char [][] wordImages = context.allWords.image;
final char [][] stemImages = new char [wordImages.length] [];
final MutableCharArray mutableCharArray = new MutableCharArray(CharArrayUtils.EMPTY_ARRAY);
char [] buffer = new char [128];
for (int i = 0; i < wordImages.length; i++)
{
final char [] word = wordImages[i];
if (buffer.length < word.length) buffer = new char [word.length];
final boolean different = CharArrayUtils.toLowerCase(word, buffer);
mutableCharArray.reset(buffer, 0, word.length);
final CharSequence stemmed = stemmer.stem(mutableCharArray);
if (stemmed != null)
{
mutableCharArray.reset(stemmed);
stemImages[i] = context.intern(mutableCharArray);
}
else
{
// We need to put the original word here, otherwise, we wouldn't be able
// to compute frequencies for stems.
if (different)
stemImages[i] = context.intern(mutableCharArray);
else
stemImages[i] = word;
}
}
addStemStatistics(context, stemImages, prepareQueryWords(context.query, stemmer));
}
/**
* Adds frequency statistics to the stems.
*/
private void addStemStatistics(PreprocessingContext context,
char [][] wordStemImages, Set<MutableCharArray> queryStems)
{
final int [] stemImagesOrder = IndirectSort.mergesort(wordStemImages, 0, wordStemImages.length,
CharArrayComparators.FAST_CHAR_ARRAY_COMPARATOR);
// Local array references
final int [] wordTfArray = context.allWords.tf;
final int [][] wordTfByDocumentArray = context.allWords.tfByDocument;
final byte [] wordsFieldIndices = context.allWords.fieldIndices;
final short [] wordsType = context.allWords.type;
final int allWordsCount = wordTfArray.length;
// Pointers from AllWords to AllStems
final int [] stemIndexesArray = new int [allWordsCount];
if (stemImagesOrder.length == 0)
{
context.allStems.image = new char [0] [];
context.allStems.mostFrequentOriginalWordIndex = new int [0];
context.allStems.tf = new int [0];
context.allStems.tfByDocument = new int [0] [];
context.allStems.fieldIndices = new byte [0];
context.allWords.stemIndex = new int [context.allWords.image.length];
return;
}
// Lists to accommodate the results
final ArrayList<char []> stemImages = new ArrayList<char []>(allWordsCount);
final IntArrayList stemTf = new IntArrayList(allWordsCount);
final IntArrayList stemMostFrequentWordIndexes = new IntArrayList(allWordsCount);
final ArrayList<int []> stemTfByDocumentList = new ArrayList<int []>(allWordsCount);
final ByteArrayList fieldIndexList = new ByteArrayList();
// Counters
int totalTf = wordTfArray[stemImagesOrder[0]];
int mostFrequentWordFrequency = wordTfArray[stemImagesOrder[0]];
int mostFrequentWordIndex = stemImagesOrder[0];
int stemIndex = 0;
// A list of document-term-frequency pairs, by document, for all words with identical stems.
final ArrayList<int[]> stemTfsByDocument = Lists.newArrayList();
stemTfsByDocument.add(wordTfByDocumentArray[stemImagesOrder[0]]);
byte fieldIndices = 0;
fieldIndices |= wordsFieldIndices[0];
// For locating query words
final MutableCharArray buffer = new MutableCharArray(
wordStemImages[stemImagesOrder[0]]);
boolean inQuery = queryStems.contains(buffer);
// Go through all words in the order of stem images
for (int i = 0; i < stemImagesOrder.length - 1; i++)
{
final int orderIndex = stemImagesOrder[i];
final char [] stem = wordStemImages[orderIndex];
final int nextInOrderIndex = stemImagesOrder[i + 1];
final char [] nextStem = wordStemImages[nextInOrderIndex];
stemIndexesArray[orderIndex] = stemIndex;
if (inQuery)
{
wordsType[orderIndex] |= ITokenizer.TF_QUERY_WORD;
}
// Now check if token image is changing
final boolean sameStem = CharArrayComparators.FAST_CHAR_ARRAY_COMPARATOR
.compare(stem, nextStem) == 0;
if (sameStem)
{
totalTf += wordTfArray[nextInOrderIndex];
stemTfsByDocument.add(wordTfByDocumentArray[nextInOrderIndex]);
fieldIndices |= wordsFieldIndices[nextInOrderIndex];
if (mostFrequentWordFrequency < wordTfArray[nextInOrderIndex])
{
mostFrequentWordFrequency = wordTfArray[nextInOrderIndex];
mostFrequentWordIndex = nextInOrderIndex;
}
}
else
{
stemImages.add(stem);
stemTf.add(totalTf);
stemMostFrequentWordIndexes.add(mostFrequentWordIndex);
storeTfByDocument(stemTfByDocumentList, stemTfsByDocument);
fieldIndexList.add(fieldIndices);
stemIndex++;
totalTf = wordTfArray[nextInOrderIndex];
mostFrequentWordFrequency = wordTfArray[nextInOrderIndex];
mostFrequentWordIndex = nextInOrderIndex;
fieldIndices = 0;
fieldIndices |= wordsFieldIndices[nextInOrderIndex];
stemTfsByDocument.clear();
stemTfsByDocument.add(wordTfByDocumentArray[nextInOrderIndex]);
buffer.reset(wordStemImages[nextInOrderIndex]);
inQuery = queryStems.contains(buffer);
}
}
// Store tf for the last stem in the array
stemImages.add(wordStemImages[stemImagesOrder[stemImagesOrder.length - 1]]);
stemTf.add(totalTf);
stemMostFrequentWordIndexes.add(mostFrequentWordIndex);
stemIndexesArray[stemImagesOrder[stemImagesOrder.length - 1]] = stemIndex;
storeTfByDocument(stemTfByDocumentList, stemTfsByDocument);
fieldIndexList.add(fieldIndices);
if (inQuery)
{
wordsType[stemImagesOrder[stemImagesOrder.length - 1]] |= ITokenizer.TF_QUERY_WORD;
}
// Convert lists to arrays and store them in allStems
context.allStems.image = stemImages.toArray(new char [stemImages.size()] []);
context.allStems.mostFrequentOriginalWordIndex = stemMostFrequentWordIndexes
.toArray();
context.allStems.tf = stemTf.toArray();
context.allStems.tfByDocument = stemTfByDocumentList
.toArray(new int [stemTfByDocumentList.size()] []);
context.allStems.fieldIndices = fieldIndexList.toArray();
// References in allWords
context.allWords.stemIndex = stemIndexesArray;
}
/**
*
*/
private void storeTfByDocument(
ArrayList<int []> target, ArrayList<int []> source)
{
assert source.size() > 0 : "Empty source document list?";
if (source.size() == 1)
{
// Just copy the reference over if a single list is available.
target.add(source.get(0));
}
else
{
// Merge sparse representations if more than one.
target.add(SparseArray.mergeSparseArrays(source));
}
}
private Set<MutableCharArray> prepareQueryWords(String query, IStemmer stemmer)
{
final Set<MutableCharArray> queryWords = Sets.newHashSet();
if (query != null)
{
final String [] split = query.toLowerCase().split("\\s");
for (int i = 0; i < split.length; i++)
{
final CharSequence stem = stemmer.stem(split[i]);
if (stem != null)
{
queryWords.add(new MutableCharArray(stem));
}
else
{
queryWords.add(new MutableCharArray(split[i]));
}
}
}
return queryWords;
}
}