org.apache.lucene.index.pruning

Class TFTermPruningPolicy

java.lang.Object

org.apache.lucene.index.pruning.PruningPolicy

org.apache.lucene.index.pruning.TermPruningPolicy

org.apache.lucene.index.pruning.TFTermPruningPolicy

public class TFTermPruningPolicy
extends TermPruningPolicy

Policy for producing smaller index out of an input index, by removing postings data for those terms where their in-document frequency is below a specified threshold.

Larger threshold value will produce a smaller index. See TermPruningPolicy for size vs performance considerations.

This implementation uses simple term frequency thresholds to remove all postings from documents where a given term occurs rarely (i.e. its TF in a document is smaller than the threshold).

Threshold values in this method are expressed as absolute term frequencies.

Field Summary

Fields

Modifier and Type	Field and Description
protected int	curThr
protected int	defThreshold
protected java.util.Map<java.lang.String,java.lang.Integer>	thresholds

Fields inherited from class org.apache.lucene.index.pruning.TermPruningPolicy

fieldFlags, in

Fields inherited from class org.apache.lucene.index.pruning.PruningPolicy

DEL_ALL, DEL_PAYLOADS, DEL_POSTINGS, DEL_STORED, DEL_VECTOR

Constructor Summary

Constructors

Constructor and Description
TFTermPruningPolicy(IndexReader in, java.util.Map<java.lang.String,java.lang.Integer> fieldFlags, java.util.Map<java.lang.String,java.lang.Integer> thresholds, int defThreshold)

Method Summary

Modifier and Type	Method and Description
void	initPositionsTerm(TermPositions in, Term t) Called when moving TermPositions to a new Term.
boolean	pruneAllPositions(TermPositions termPositions, Term t) Prune all postings per term (invoked once per term per doc)
int	pruneSomePositions(int docNum, int[] positions, Term curTerm) Prune some postings per term (invoked once per term per doc).
boolean	pruneTermEnum(TermEnum te) Pruning of all postings for a term (invoked once per term).
int	pruneTermVectorTerms(int docNumber, java.lang.String field, java.lang.String[] terms, int[] freqs, TermFreqVector tfv) Pruning of individual terms in term vectors.

Methods inherited from class org.apache.lucene.index.pruning.TermPruningPolicy

pruneAllFieldPostings, prunePayload, pruneWholeTermVector

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

thresholds

protected java.util.Map<java.lang.String,java.lang.Integer> thresholds

defThreshold

protected int defThreshold

curThr

protected int curThr

Constructor Detail

TFTermPruningPolicy

public TFTermPruningPolicy(IndexReader in,
                           java.util.Map<java.lang.String,java.lang.Integer> fieldFlags,
                           java.util.Map<java.lang.String,java.lang.Integer> thresholds,
                           int defThreshold)

Method Detail

pruneTermEnum

public boolean pruneTermEnum(TermEnum te)
                      throws java.io.IOException

Description copied from class: TermPruningPolicy

Pruning of all postings for a term (invoked once per term).

Specified by:

pruneTermEnum in class TermPruningPolicy

Parameters:

te - positioned term enum.

Returns:

true if all postings for this term should be removed, false otherwise.

Throws:

java.io.IOException

initPositionsTerm

public void initPositionsTerm(TermPositions in,
                              Term t)
                       throws java.io.IOException

Description copied from class: TermPruningPolicy

Called when moving TermPositions to a new Term.

Specified by:

initPositionsTerm in class TermPruningPolicy

Parameters:

in - input term positions

t - current term

Throws:

java.io.IOException

pruneAllPositions

public boolean pruneAllPositions(TermPositions termPositions,
                                 Term t)
                          throws java.io.IOException

Description copied from class: TermPruningPolicy

Prune all postings per term (invoked once per term per doc)

Specified by:

pruneAllPositions in class TermPruningPolicy

Parameters:

termPositions - positioned term positions. Implementations MUST NOT advance this by calling TermPositions methods that advance either the position pointer (next, skipTo) or term pointer (seek).

t - current term

Returns:

true if the current posting should be removed, false otherwise.

Throws:

java.io.IOException

pruneTermVectorTerms

public int pruneTermVectorTerms(int docNumber,
                                java.lang.String field,
                                java.lang.String[] terms,
                                int[] freqs,
                                TermFreqVector tfv)
                         throws java.io.IOException

Description copied from class: TermPruningPolicy

Pruning of individual terms in term vectors.

Specified by:

pruneTermVectorTerms in class TermPruningPolicy

Parameters:

docNumber - document number

field - field name

terms - array of terms

freqs - array of term frequencies

tfv - the original term frequency vector

Returns:

0 if no terms are to be removed, positive number to indicate how many terms need to be removed. The same number of entries in the terms array must be set to null to indicate which terms to remove.

Throws:

java.io.IOException

pruneSomePositions

public int pruneSomePositions(int docNum,
                              int[] positions,
                              Term curTerm)

Description copied from class: TermPruningPolicy

Prune some postings per term (invoked once per term per doc).

Specified by:

pruneSomePositions in class TermPruningPolicy

Parameters:

docNum - current document number

positions - original term positions in the document (and indirectly term frequency)

curTerm - current term

Returns:

0 if no postings are to be removed, or positive number to indicate how many postings need to be removed. The same number of entries in the positions array must be set to -1 to indicate which positions to remove.