package org.apache.lucene.analysis.shingle;
/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF 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.
*/
import java.io.IOException;
import java.util.Iterator;
import java.util.LinkedList;
import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.OffsetAttribute;
import org.apache.lucene.analysis.tokenattributes.PositionIncrementAttribute;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.analysis.tokenattributes.TypeAttribute;
import org.apache.lucene.util.AttributeSource;
/**
* <p>A ShingleFilter constructs shingles (token n-grams) from a token stream.
* In other words, it creates combinations of tokens as a single token.
*
* <p>For example, the sentence "please divide this sentence into shingles"
* might be tokenized into shingles "please divide", "divide this",
* "this sentence", "sentence into", and "into shingles".
*
* <p>This filter handles position increments > 1 by inserting filler tokens
* (tokens with termtext "_"). It does not handle a position increment of 0.
*/
public final class ShingleFilter extends TokenFilter {
/**
* filler token for when positionIncrement is more than 1
*/
public static final char[] FILLER_TOKEN = { '_' };
/**
* default maximum shingle size is 2.
*/
public static final int DEFAULT_MAX_SHINGLE_SIZE = 2;
/**
* default minimum shingle size is 2.
*/
public static final int DEFAULT_MIN_SHINGLE_SIZE = 2;
/**
* default token type attribute value is "shingle"
*/
public static final String DEFAULT_TOKEN_TYPE = "shingle";
/**
* The default string to use when joining adjacent tokens to form a shingle
*/
public static final String TOKEN_SEPARATOR = " ";
/**
* The sequence of input stream tokens (or filler tokens, if necessary)
* that will be composed to form output shingles.
*/
private LinkedList<InputWindowToken> inputWindow
= new LinkedList<InputWindowToken>();
/**
* The number of input tokens in the next output token. This is the "n" in
* "token n-grams".
*/
private CircularSequence gramSize;
/**
* Shingle and unigram text is composed here.
*/
private StringBuilder gramBuilder = new StringBuilder();
/**
* The token type attribute value to use - default is "shingle"
*/
private String tokenType = DEFAULT_TOKEN_TYPE;
/**
* The string to use when joining adjacent tokens to form a shingle
*/
private String tokenSeparator = TOKEN_SEPARATOR;
/**
* By default, we output unigrams (individual tokens) as well as shingles
* (token n-grams).
*/
private boolean outputUnigrams = true;
/**
* maximum shingle size (number of tokens)
*/
private int maxShingleSize;
/**
* minimum shingle size (number of tokens)
*/
private int minShingleSize;
/**
* The remaining number of filler tokens to be inserted into the input stream
* from which shingles are composed, to handle position increments greater
* than one.
*/
private int numFillerTokensToInsert;
/**
* When the next input stream token has a position increment greater than
* one, it is stored in this field until sufficient filler tokens have been
* inserted to account for the position increment.
*/
private AttributeSource nextInputStreamToken;
/**
* Whether or not there is a next input stream token.
*/
private boolean isNextInputStreamToken = false;
/**
* Whether at least one unigram or shingle has been output at the current
* position.
*/
private boolean isOutputHere = false;
private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
private final OffsetAttribute offsetAtt = addAttribute(OffsetAttribute.class);
private final PositionIncrementAttribute posIncrAtt = addAttribute(PositionIncrementAttribute.class);
private final TypeAttribute typeAtt = addAttribute(TypeAttribute.class);
/**
* Constructs a ShingleFilter with the specified shingle size from the
* {@link TokenStream} <code>input</code>
*
* @param input input stream
* @param minShingleSize minimum shingle size produced by the filter.
* @param maxShingleSize maximum shingle size produced by the filter.
*/
public ShingleFilter(TokenStream input, int minShingleSize, int maxShingleSize) {
super(input);
setMaxShingleSize(maxShingleSize);
setMinShingleSize(minShingleSize);
}
/**
* Constructs a ShingleFilter with the specified shingle size from the
* {@link TokenStream} <code>input</code>
*
* @param input input stream
* @param maxShingleSize maximum shingle size produced by the filter.
*/
public ShingleFilter(TokenStream input, int maxShingleSize) {
this(input, DEFAULT_MIN_SHINGLE_SIZE, maxShingleSize);
}
/**
* Construct a ShingleFilter with default shingle size: 2.
*
* @param input input stream
*/
public ShingleFilter(TokenStream input) {
this(input, DEFAULT_MIN_SHINGLE_SIZE, DEFAULT_MAX_SHINGLE_SIZE);
}
/**
* Construct a ShingleFilter with the specified token type for shingle tokens
* and the default shingle size: 2
*
* @param input input stream
* @param tokenType token type for shingle tokens
*/
public ShingleFilter(TokenStream input, String tokenType) {
this(input, DEFAULT_MIN_SHINGLE_SIZE, DEFAULT_MAX_SHINGLE_SIZE);
setTokenType(tokenType);
}
/**
* Set the type of the shingle tokens produced by this filter.
* (default: "shingle")
*
* @param tokenType token tokenType
*/
public void setTokenType(String tokenType) {
this.tokenType = tokenType;
}
/**
* Shall the output stream contain the input tokens (unigrams) as well as
* shingles? (default: true.)
*
* @param outputUnigrams Whether or not the output stream shall contain
* the input tokens (unigrams)
*/
public void setOutputUnigrams(boolean outputUnigrams) {
this.outputUnigrams = outputUnigrams;
gramSize = new CircularSequence();
}
/**
* Set the max shingle size (default: 2)
*
* @param maxShingleSize max size of output shingles
*/
public void setMaxShingleSize(int maxShingleSize) {
if (maxShingleSize < 2) {
throw new IllegalArgumentException("Max shingle size must be >= 2");
}
this.maxShingleSize = maxShingleSize;
}
/**
* <p>Set the min shingle size (default: 2).
* <p>This method requires that the passed in minShingleSize is not greater
* than maxShingleSize, so make sure that maxShingleSize is set before
* calling this method.
* <p>The unigram output option is independent of the min shingle size.
*
* @param minShingleSize min size of output shingles
*/
public void setMinShingleSize(int minShingleSize) {
if (minShingleSize < 2) {
throw new IllegalArgumentException("Min shingle size must be >= 2");
}
if (minShingleSize > maxShingleSize) {
throw new IllegalArgumentException
("Min shingle size must be <= max shingle size");
}
this.minShingleSize = minShingleSize;
gramSize = new CircularSequence();
}
/**
* Sets the string to use when joining adjacent tokens to form a shingle
* @param tokenSeparator used to separate input stream tokens in output shingles
*/
public void setTokenSeparator(String tokenSeparator) {
this.tokenSeparator = null == tokenSeparator ? "" : tokenSeparator;
}
@Override
public final boolean incrementToken() throws IOException {
boolean tokenAvailable = false;
int builtGramSize = 0;
if (gramSize.atMinValue() || inputWindow.size() < gramSize.getValue()) {
shiftInputWindow();
gramBuilder.setLength(0);
} else {
builtGramSize = gramSize.getPreviousValue();
}
if (inputWindow.size() >= gramSize.getValue()) {
boolean isAllFiller = true;
InputWindowToken nextToken = null;
Iterator<InputWindowToken> iter = inputWindow.iterator();
for (int gramNum = 1 ;
iter.hasNext() && builtGramSize < gramSize.getValue() ;
++gramNum) {
nextToken = iter.next();
if (builtGramSize < gramNum) {
if (builtGramSize > 0) {
gramBuilder.append(tokenSeparator);
}
gramBuilder.append(nextToken.termAtt.buffer(), 0,
nextToken.termAtt.length());
++builtGramSize;
}
if (isAllFiller && nextToken.isFiller) {
if (gramNum == gramSize.getValue()) {
gramSize.advance();
}
} else {
isAllFiller = false;
}
}
if ( ! isAllFiller && builtGramSize == gramSize.getValue()) {
inputWindow.getFirst().attSource.copyTo(this);
posIncrAtt.setPositionIncrement(isOutputHere ? 0 : 1);
termAtt.setEmpty().append(gramBuilder);
if (gramSize.getValue() > 1) {
typeAtt.setType(tokenType);
}
offsetAtt.setOffset(offsetAtt.startOffset(), nextToken.offsetAtt.endOffset());
isOutputHere = true;
gramSize.advance();
tokenAvailable = true;
}
}
return tokenAvailable;
}
/**
* <p>Get the next token from the input stream.
* <p>If the next token has <code>positionIncrement > 1</code>,
* <code>positionIncrement - 1</code> {@link #FILLER_TOKEN}s are
* inserted first.
* @param target Where to put the new token; if null, a new instance is created.
* @return On success, the populated token; null otherwise
* @throws IOException if the input stream has a problem
*/
private InputWindowToken getNextToken(InputWindowToken target)
throws IOException {
InputWindowToken newTarget = target;
if (numFillerTokensToInsert > 0) {
if (null == target) {
newTarget = new InputWindowToken(nextInputStreamToken.cloneAttributes());
} else {
nextInputStreamToken.copyTo(target.attSource);
}
// A filler token occupies no space
newTarget.offsetAtt.setOffset(newTarget.offsetAtt.startOffset(),
newTarget.offsetAtt.startOffset());
newTarget.termAtt.copyBuffer(FILLER_TOKEN, 0, FILLER_TOKEN.length);
newTarget.isFiller = true;
--numFillerTokensToInsert;
} else if (isNextInputStreamToken) {
if (null == target) {
newTarget = new InputWindowToken(nextInputStreamToken.cloneAttributes());
} else {
nextInputStreamToken.copyTo(target.attSource);
}
isNextInputStreamToken = false;
newTarget.isFiller = false;
} else if (input.incrementToken()) {
if (null == target) {
newTarget = new InputWindowToken(cloneAttributes());
} else {
this.copyTo(target.attSource);
}
if (posIncrAtt.getPositionIncrement() > 1) {
// Each output shingle must contain at least one input token,
// so no more than (maxShingleSize - 1) filler tokens will be inserted.
numFillerTokensToInsert
= Math.min(posIncrAtt.getPositionIncrement() - 1, maxShingleSize - 1);
// Save the current token as the next input stream token
if (null == nextInputStreamToken) {
nextInputStreamToken = cloneAttributes();
} else {
this.copyTo(nextInputStreamToken);
}
isNextInputStreamToken = true;
// A filler token occupies no space
newTarget.offsetAtt.setOffset(offsetAtt.startOffset(), offsetAtt.startOffset());
newTarget.termAtt.copyBuffer(FILLER_TOKEN, 0, FILLER_TOKEN.length);
newTarget.isFiller = true;
--numFillerTokensToInsert;
} else {
newTarget.isFiller = false;
}
} else {
newTarget = null;
}
return newTarget;
}
/**
* <p>Fills {@link #inputWindow} with input stream tokens, if available,
* shifting to the right if the window was previously full.
* <p>Resets {@link #gramSize} to its minimum value.
*
* @throws IOException if there's a problem getting the next token
*/
private void shiftInputWindow() throws IOException {
InputWindowToken firstToken = null;
if (inputWindow.size() > 0) {
firstToken = inputWindow.removeFirst();
}
while (inputWindow.size() < maxShingleSize) {
if (null != firstToken) { // recycle the firstToken, if available
if (null != getNextToken(firstToken)) {
inputWindow.add(firstToken); // the firstToken becomes the last
firstToken = null;
} else {
break; // end of input stream
}
} else {
InputWindowToken nextToken = getNextToken(null);
if (null != nextToken) {
inputWindow.add(nextToken);
} else {
break; // end of input stream
}
}
}
gramSize.reset();
isOutputHere = false;
}
@Override
public void reset() throws IOException {
super.reset();
gramSize.reset();
inputWindow.clear();
numFillerTokensToInsert = 0;
isOutputHere = false;
}
/**
* <p>An instance of this class is used to maintain the number of input
* stream tokens that will be used to compose the next unigram or shingle:
* {@link #gramSize}.
* <p><code>gramSize</code> will take on values from the circular sequence
* <b>{ [ 1, ] {@link #minShingleSize} [ , ... , {@link #maxShingleSize} ] }</b>.
* <p>1 is included in the circular sequence only if
* {@link #outputUnigrams} = true.
*/
private class CircularSequence {
private int value;
private int previousValue;
private int minValue;
public CircularSequence() {
minValue = outputUnigrams ? 1 : minShingleSize;
reset();
}
/**
* @return the current value.
* @see #advance()
*/
public int getValue() {
return value;
}
/**
* <p>Increments this circular number's value to the next member in the
* circular sequence
* <code>gramSize</code> will take on values from the circular sequence
* <b>{ [ 1, ] {@link #minShingleSize} [ , ... , {@link #maxShingleSize} ] }</b>.
* <p>1 is included in the circular sequence only if
* {@link #outputUnigrams} = true.
*/
public void advance() {
previousValue = value;
if (value == 1) {
value = minShingleSize;
} else if (value == maxShingleSize) {
reset();
} else {
++value;
}
}
/**
* <p>Sets this circular number's value to the first member of the
* circular sequence
* <p><code>gramSize</code> will take on values from the circular sequence
* <b>{ [ 1, ] {@link #minShingleSize} [ , ... , {@link #maxShingleSize} ] }</b>.
* <p>1 is included in the circular sequence only if
* {@link #outputUnigrams} = true.
*/
public void reset() {
previousValue = value = minValue;
}
/**
* <p>Returns true if the current value is the first member of the circular
* sequence.
* <p>If {@link #outputUnigrams} = true, the first member of the circular
* sequence will be 1; otherwise, it will be {@link #minShingleSize}.
*
* @return true if the current value is the first member of the circular
* sequence; false otherwise
*/
public boolean atMinValue() {
return value == minValue;
}
/**
* @return the value this instance had before the last advance() call
*/
public int getPreviousValue() {
return previousValue;
}
}
private class InputWindowToken {
final AttributeSource attSource;
final CharTermAttribute termAtt;
final OffsetAttribute offsetAtt;
boolean isFiller = false;
public InputWindowToken(AttributeSource attSource) {
this.attSource = attSource;
this.termAtt = attSource.getAttribute(CharTermAttribute.class);
this.offsetAtt = attSource.getAttribute(OffsetAttribute.class);
}
}
}