org.apache.lucene.analysis.shingle
Class ShingleFilter

java.lang.Object
  org.apache.lucene.util.AttributeSource
      org.apache.lucene.analysis.TokenStream
          org.apache.lucene.analysis.TokenFilter
              org.apache.lucene.analysis.shingle.ShingleFilter

All Implemented Interfaces:

Closeable

public final class ShingleFilter
extends TokenFilter

A ShingleFilter constructs shingles (token n-grams) from a token stream. In other words, it creates combinations of tokens as a single token.

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".

This filter handles position increments > 1 by inserting filler tokens (tokens with termtext "_"). It does not handle a position increment of 0.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.lucene.util.AttributeSource

AttributeSource.AttributeFactory, AttributeSource.State

Field Summary

static int	DEFAULT_MAX_SHINGLE_SIZE default maximum shingle size is 2.
static int	DEFAULT_MIN_SHINGLE_SIZE default minimum shingle size is 2.
static String	DEFAULT_TOKEN_TYPE default token type attribute value is "shingle"
static char[]	FILLER_TOKEN filler token for when positionIncrement is more than 1
static String	TOKEN_SEPARATOR The default string to use when joining adjacent tokens to form a shingle

Fields inherited from class org.apache.lucene.analysis.TokenFilter

input

Constructor Summary

ShingleFilter(TokenStream input)
Construct a ShingleFilter with default shingle size: 2.

ShingleFilter(TokenStream input, int maxShingleSize)
Constructs a ShingleFilter with the specified shingle size from the TokenStream input

ShingleFilter(TokenStream input, int minShingleSize, int maxShingleSize)
Constructs a ShingleFilter with the specified shingle size from the TokenStream input

ShingleFilter(TokenStream input, String tokenType)
Construct a ShingleFilter with the specified token type for shingle tokens and the default shingle size: 2

Method Summary

boolean	incrementToken() Consumers (i.e., IndexWriter) use this method to advance the stream to the next token.
void	reset() Reset the filter as well as the input TokenStream.
void	setMaxShingleSize(int maxShingleSize) Set the max shingle size (default: 2)
void	setMinShingleSize(int minShingleSize) Set the min shingle size (default: 2).
void	setOutputUnigrams(boolean outputUnigrams) Shall the output stream contain the input tokens (unigrams) as well as shingles? (default: true.)
void	setOutputUnigramsIfNoShingles(boolean outputUnigramsIfNoShingles) Shall we override the behavior of outputUnigrams==false for those times when no shingles are available (because there are fewer than minShingleSize tokens in the input stream)? (default: false.)
void	setTokenSeparator(String tokenSeparator) Sets the string to use when joining adjacent tokens to form a shingle
void	setTokenType(String tokenType) Set the type of the shingle tokens produced by this filter.

Methods inherited from class org.apache.lucene.analysis.TokenFilter

close, end

Methods inherited from class org.apache.lucene.util.AttributeSource

addAttribute, addAttributeImpl, captureState, clearAttributes, cloneAttributes, copyTo, equals, getAttribute, getAttributeClassesIterator, getAttributeFactory, getAttributeImplsIterator, hasAttribute, hasAttributes, hashCode, reflectAsString, reflectWith, restoreState, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

FILLER_TOKEN

public static final char[] FILLER_TOKEN

filler token for when positionIncrement is more than 1

DEFAULT_MAX_SHINGLE_SIZE

public static final int DEFAULT_MAX_SHINGLE_SIZE

default maximum shingle size is 2.

See Also:

Constant Field Values

DEFAULT_MIN_SHINGLE_SIZE

public static final int DEFAULT_MIN_SHINGLE_SIZE

default minimum shingle size is 2.

See Also:

Constant Field Values

DEFAULT_TOKEN_TYPE

public static final String DEFAULT_TOKEN_TYPE

default token type attribute value is "shingle"

See Also:

Constant Field Values

TOKEN_SEPARATOR

public static final String TOKEN_SEPARATOR

The default string to use when joining adjacent tokens to form a shingle

See Also:

Constant Field Values

Constructor Detail

ShingleFilter

public ShingleFilter(TokenStream input,
                     int minShingleSize,
                     int maxShingleSize)

Constructs a ShingleFilter with the specified shingle size from the TokenStream input

Parameters:

input - input stream

minShingleSize - minimum shingle size produced by the filter.

maxShingleSize - maximum shingle size produced by the filter.

ShingleFilter

public ShingleFilter(TokenStream input,
                     int maxShingleSize)

Constructs a ShingleFilter with the specified shingle size from the TokenStream input

Parameters:

input - input stream

maxShingleSize - maximum shingle size produced by the filter.

ShingleFilter

public ShingleFilter(TokenStream input)

Construct a ShingleFilter with default shingle size: 2.

Parameters:

input - input stream

ShingleFilter

public ShingleFilter(TokenStream input,
                     String tokenType)

Construct a ShingleFilter with the specified token type for shingle tokens and the default shingle size: 2

Parameters:

input - input stream

tokenType - token type for shingle tokens

Method Detail

setTokenType

public void setTokenType(String tokenType)

Set the type of the shingle tokens produced by this filter. (default: "shingle")

Parameters:

tokenType - token tokenType

setOutputUnigrams

public void setOutputUnigrams(boolean outputUnigrams)

Shall the output stream contain the input tokens (unigrams) as well as shingles? (default: true.)

Parameters:

outputUnigrams - Whether or not the output stream shall contain the input tokens (unigrams)

setOutputUnigramsIfNoShingles

public void setOutputUnigramsIfNoShingles(boolean outputUnigramsIfNoShingles)

Shall we override the behavior of outputUnigrams==false for those times when no shingles are available (because there are fewer than minShingleSize tokens in the input stream)? (default: false.)

Note that if outputUnigrams==true, then unigrams are always output, regardless of whether any shingles are available.

Parameters:

outputUnigramsIfNoShingles - Whether or not to output a single unigram when no shingles are available.

setMaxShingleSize

public void setMaxShingleSize(int maxShingleSize)

Set the max shingle size (default: 2)

Parameters:

maxShingleSize - max size of output shingles

setMinShingleSize

public void setMinShingleSize(int minShingleSize)

Set the min shingle size (default: 2).

This method requires that the passed in minShingleSize is not greater than maxShingleSize, so make sure that maxShingleSize is set before calling this method.

The unigram output option is independent of the min shingle size.

Parameters:

minShingleSize - min size of output shingles

setTokenSeparator

public void setTokenSeparator(String tokenSeparator)

Sets the string to use when joining adjacent tokens to form a shingle

Parameters:

tokenSeparator - used to separate input stream tokens in output shingles

incrementToken

public final boolean incrementToken()
                             throws IOException

Description copied from class: TokenStream

Consumers (i.e., IndexWriter) use this method to advance the stream to the next token. Implementing classes must implement this method and update the appropriate AttributeImpls with the attributes of the next token.

The producer must make no assumptions about the attributes after the method has been returned: the caller may arbitrarily change it. If the producer needs to preserve the state for subsequent calls, it can use AttributeSource.captureState() to create a copy of the current attribute state.

This method is called for every token of a document, so an efficient implementation is crucial for good performance. To avoid calls to AttributeSource.addAttribute(Class) and AttributeSource.getAttribute(Class), references to all AttributeImpls that this stream uses should be retrieved during instantiation.

To ensure that filters and consumers know which attributes are available, the attributes must be added during instantiation. Filters and consumers are not required to check for availability of attributes in TokenStream.incrementToken().

Specified by:

incrementToken in class TokenStream

Returns:

false for end of stream; true otherwise

Throws:

IOException

reset

public void reset()
           throws IOException

Description copied from class: TokenFilter

Reset the filter as well as the input TokenStream.

Overrides:

reset in class TokenFilter

Throws:

IOException