Package org.apache.lucene.index.pruning
Class RIDFTermPruningPolicy
- java.lang.Object
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- org.apache.lucene.index.pruning.PruningPolicy
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- org.apache.lucene.index.pruning.TermPruningPolicy
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- org.apache.lucene.index.pruning.RIDFTermPruningPolicy
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public class RIDFTermPruningPolicy extends TermPruningPolicy
Implementation ofTermPruningPolicy
that uses "residual IDF" metric to determine the postings of terms to keep/remove, as defined in http://www.dc.fi.udc.es/~barreiro/publications/blanco_barreiro_ecir2007.pdf.Residual IDF measures a difference between a collection-wide IDF of a term (which assumes a uniform distribution of occurrences) and the actual observed total number of occurrences of a term in all documents. Positive values indicate that a term is informative (e.g. for rare terms), negative values indicate that a term is not informative (e.g. too popular to offer good selectivity).
This metric produces small values close to [-1, 1], so useful ranges for thresholds under this metrics are somewhere between [0, 1]. The higher the threshold the more informative (and more rare) terms will be retained. For filtering of common words a value of close to or slightly below 0 (e.g. -0.1) should be a good starting point.
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Field Summary
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Fields inherited from class org.apache.lucene.index.pruning.TermPruningPolicy
fieldFlags, in
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Fields inherited from class org.apache.lucene.index.pruning.PruningPolicy
DEL_ALL, DEL_PAYLOADS, DEL_POSTINGS, DEL_STORED, DEL_VECTOR
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Constructor Summary
Constructors Constructor Description RIDFTermPruningPolicy(IndexReader in, Map<String,Integer> fieldFlags, Map<String,Double> thresholds, double defThreshold)
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
initPositionsTerm(TermPositions tp, Term t)
Called when movingTermPositions
to a newTerm
.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, String field, String[] terms, int[] freqs, TermFreqVector v)
Pruning of individual terms in term vectors.-
Methods inherited from class org.apache.lucene.index.pruning.TermPruningPolicy
pruneAllFieldPostings, prunePayload, pruneWholeTermVector
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Method Detail
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initPositionsTerm
public void initPositionsTerm(TermPositions tp, Term t) throws IOException
Description copied from class:TermPruningPolicy
Called when movingTermPositions
to a newTerm
.- Specified by:
initPositionsTerm
in classTermPruningPolicy
- Parameters:
tp
- input term positionst
- current term- Throws:
IOException
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pruneTermEnum
public boolean pruneTermEnum(TermEnum te) throws IOException
Description copied from class:TermPruningPolicy
Pruning of all postings for a term (invoked once per term).- Specified by:
pruneTermEnum
in classTermPruningPolicy
- Parameters:
te
- positioned term enum.- Returns:
- true if all postings for this term should be removed, false otherwise.
- Throws:
IOException
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pruneAllPositions
public boolean pruneAllPositions(TermPositions termPositions, Term t) throws IOException
Description copied from class:TermPruningPolicy
Prune all postings per term (invoked once per term per doc)- Specified by:
pruneAllPositions
in classTermPruningPolicy
- Parameters:
termPositions
- positioned term positions. Implementations MUST NOT advance this by callingTermPositions
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:
IOException
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pruneTermVectorTerms
public int pruneTermVectorTerms(int docNumber, String field, String[] terms, int[] freqs, TermFreqVector v) throws IOException
Description copied from class:TermPruningPolicy
Pruning of individual terms in term vectors.- Specified by:
pruneTermVectorTerms
in classTermPruningPolicy
- Parameters:
docNumber
- document numberfield
- field nameterms
- array of termsfreqs
- array of term frequenciesv
- 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:
IOException
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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 classTermPruningPolicy
- Parameters:
docNum
- current document numberpositions
- 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.
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