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Java Source Code / Java Documentation » Search Engine » mg4j » it.unimi.dsi.mg4j.index

Source Cross Reference Class Diagram Java Document (Java Doc)

it.unimi.dsi.mg4j.search .AbstractUnionDocumentIterator

it.unimi.dsi.mg4j.index .MultiTermIndexIterator

MultiTermIndexIterator

public class MultiTermIndexIterator extends AbstractUnionDocumentIterator implements IndexIterator(Code)

A virtual that merges several component index iterators.

This class adds to it.unimi.dsi.mg4j.search.AbstractUnionDocumentIterator an interval interator generating the OR of the intervals returned for each of the documents involved. The main difference with an OrDocumentIterator built on the same array of component iterators is that this class implements IndexIterator and hence provides a MultiTermIndexIterator.count() (the sum of counts of those component iterators positioned on the current document) and a MultiTermIndexIterator.frequency() . The latter is by default the maximum frequency of a component iterator, but it can be set at MultiTermIndexIterator.getInstance(intIndexIndexIterator[]) construction time .

The main raison d'être of this class is support for query expansion: a blind application of OrDocumentIterator to an array of index iterators would mislead scorers such as BM25Scorer because low-frequency terms (e.g., hapax legomena) would be responsible for most of the score.

Field Summary
protected int	id The id of this iterator.
protected String	term The term of this iterator.

Constructor Summary
protected	MultiTermIndexIterator(int defaultFrequency, IndexIterator... indexIterator) Creates a new document iterator that merges the given array of iterators.

Method Summary
public boolean	accept(DocumentIteratorVisitor visitor)
public boolean	acceptOnTruePaths(DocumentIteratorVisitor visitor)
public int	count() The count is the sum of counts of those component iterators positioned on the current document.
public int	frequency() The frequency is either the default frequency set at construction time, or the maximum frequency of the component iterators.
protected IntervalIterator	getComposedIntervalIterator(Index index)
public static IndexIterator	getInstance(IndexIterator... indexIterator) Returns an index iterator that merges the given array of iterators. This method requires that at least one iterator is provided.
public static IndexIterator	getInstance(Index index, IndexIterator... indexIterator) Returns an index iterator that merges the given array of iterators. Note that the special case of the empty and of the singleton arrays are handled efficiently.
public static IndexIterator	getInstance(int defaultFrequency, IndexIterator... indexIterator) Returns an index iterator that merges the given array of iterators. This method requires that at least one iterator is provided. Parameters: defaultFrequency - the default term frequency (or Integer.MIN_VALUE for the max). Parameters: indexIterator - the iterators to be joined (at least one).
public static IndexIterator	getInstance(int defaultFrequency, Index index, IndexIterator... indexIterator) Returns an index iterator that merges the given array of iterators. Note that the special case of the empty and of the singleton arrays are handled efficiently.
public void	id(int id)
public int	id()
public Index	index()
public int	nextDocument()
public Payload	payload() This method is not implemented by this class.
public int[]	positionArray()
public IntIterator	positions()
public int	positions(int[] position)
public int	skipTo(int n)
public void	term(CharSequence term)
public String	term()
public int	termNumber()

Field Detail

id
protected int id(Code)
	The id of this iterator.

term
protected String term(Code)
	The term of this iterator.

Constructor Detail

MultiTermIndexIterator
protected MultiTermIndexIterator(int defaultFrequency, IndexIterator... indexIterator) throws IOException(Code)
	Creates a new document iterator that merges the given array of iterators. Parameters: defaultFrequency - the default term frequency (or Integer.MIN_VALUE for the max). Parameters: indexIterator - the iterators to be joined.

Method Detail

accept
public boolean accept(DocumentIteratorVisitor visitor) throws IOException(Code)

acceptOnTruePaths
public boolean acceptOnTruePaths(DocumentIteratorVisitor visitor) throws IOException(Code)

count
public int count() throws IOException(Code)
	The count is the sum of counts of those component iterators positioned on the current document. the sum of counts.

frequency
public int frequency() throws IOException(Code)
	The frequency is either the default frequency set at construction time, or the maximum frequency of the component iterators. the frequency.

getComposedIntervalIterator
protected IntervalIterator getComposedIntervalIterator(Index index)(Code)

getInstance
public static IndexIterator getInstance(IndexIterator... indexIterator) throws IOException(Code)
	Returns an index iterator that merges the given array of iterators. This method requires that at least one iterator is provided. The frequency is computed as a max, and MultiTermIndexIterator.index() will return the result of the same method on the first iterator. Parameters: indexIterator - the iterators to be joined (at least one). a merged index iterator. throws: IllegalArgumentException - if no iterators were provided.

getInstance
public static IndexIterator getInstance(Index index, IndexIterator... indexIterator) throws IOException(Code)
	Returns an index iterator that merges the given array of iterators. Note that the special case of the empty and of the singleton arrays are handled efficiently. The frequency is computed as a max, and MultiTermIndexIterator.index() will return `index`. Parameters: index - the index that wil be returned by MultiTermIndexIterator.index(). Parameters: indexIterator - the iterators to be joined. a merged index iterator.

getInstance
public static IndexIterator getInstance(int defaultFrequency, IndexIterator... indexIterator) throws IOException(Code)
	Returns an index iterator that merges the given array of iterators. This method requires that at least one iterator is provided. Parameters: defaultFrequency - the default term frequency (or Integer.MIN_VALUE for the max). Parameters: indexIterator - the iterators to be joined (at least one). a merged index iterator. throws: IllegalArgumentException - if no iterators were provided, or they run on different indices.

getInstance
public static IndexIterator getInstance(int defaultFrequency, Index index, IndexIterator... indexIterator) throws IOException(Code)
	Returns an index iterator that merges the given array of iterators. Note that the special case of the empty and of the singleton arrays are handled efficiently. Parameters: defaultFrequency - the default term frequency (or Integer.MIN_VALUE for the max). Parameters: index - the index that wil be returned by MultiTermIndexIterator.index(). Parameters: indexIterator - the iterators to be joined. a merged index iterator. throws: IllegalArgumentException - if there is some iterator on an index different from `index`.

id
public void id(int id)(Code)

id
public int id()(Code)

index
public Index index()(Code)

nextDocument
public int nextDocument() throws IOException(Code)

payload
public Payload payload()(Code)
	This method is not implemented by this class.

positionArray
public int[] positionArray() throws IOException(Code)

positions
public IntIterator positions() throws IOException(Code)

positions
public int positions(int[] position) throws IOException(Code)

skipTo
public int skipTo(int n) throws IOException(Code)

term
public void term(CharSequence term)(Code)

term
public String term()(Code)

termNumber
public int termNumber()(Code)

Fields inherited from it.unimi.dsi.mg4j.search.AbstractUnionDocumentIterator

final protected int[] curr(Code)(Java Doc)
final protected int[] front(Code)(Java Doc)
protected int frontSize(Code)(Java Doc)
final protected IntHeapSemiIndirectPriorityQueue queue(Code)(Java Doc)

Methods inherited from it.unimi.dsi.mg4j.search.AbstractUnionDocumentIterator

public boolean acceptOnTruePaths(DocumentIteratorVisitor visitor) throws IOException(Code)(Java Doc)
protected int computeFront()(Code)(Java Doc)
abstract protected IntervalIterator getComposedIntervalIterator(Index index)(Code)(Java Doc)
public IntervalIterator intervalIterator(Index index) throws IOException(Code)(Java Doc)
public Reference2ReferenceMap<Index, IntervalIterator> intervalIterators() throws IOException(Code)(Java Doc)
public int nextDocument() throws IOException(Code)(Java Doc)
public int skipTo(int n) throws IOException(Code)(Java Doc)

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