org.apache.lucene.analysis.shingle
Class ShingleFilter

java.lang.Object
  extended by org.apache.lucene.util.AttributeSource
      extended by org.apache.lucene.analysis.TokenStream
          extended by org.apache.lucene.analysis.TokenFilter
              extended by 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


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