Package it.unimi.di.big.mg4j.search

Class LowPassDocumentIterator

java.lang.Object

it.unimi.di.big.mg4j.search.AbstractDocumentIterator

it.unimi.di.big.mg4j.search.AbstractIntervalDocumentIterator

it.unimi.di.big.mg4j.search.LowPassDocumentIterator

All Implemented Interfaces:

DocumentIterator

public class LowPassDocumentIterator
extends AbstractIntervalDocumentIterator

A document iterator that filters another document iterator, returning just intervals (and containing documents) whose length does not exceed a given threshold.

Since:

0.9

Author:

Paolo Boldi, Sebastiano Vigna

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
protected class	LowPassDocumentIterator.LowPassIntervalIterator	An interval iterator returning just the interval shorter than threshold.

Field Summary

Fields

Modifier and Type	Field	Description
protected DocumentIterator	documentIterator	The underlying iterator.
protected int	threshold	The iterator threshold.

Fields inherited from class it.unimi.di.big.mg4j.search.AbstractIntervalDocumentIterator

currentIterators, indices, intervalIterators, soleIndex, soleIntervalIterator, unmodifiableCurrentIterators

Fields inherited from class it.unimi.di.big.mg4j.search.AbstractDocumentIterator

curr, weight

Fields inherited from interface it.unimi.di.big.mg4j.search.DocumentIterator

END_OF_LIST

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	LowPassDocumentIterator(DocumentIterator documentIterator, int threshold)	Creates a new low-pass document iterator over a given iterator.

Method Summary

Modifier and Type	Method	Description
<T> T	accept(DocumentIteratorVisitor<T> visitor)	Accepts a visitor.
<T> T	acceptOnTruePaths(DocumentIteratorVisitor<T> visitor)	Accepts a visitor after a call to DocumentIterator.nextDocument(), limiting recursion to true paths.
void	dispose()	Disposes this document iterator, releasing all resources.
static LowPassDocumentIterator	getInstance(DocumentIterator it, int threshold)	Returns a low-pass document iterator over a given iterator.
protected IntervalIterator	getIntervalIterator(Index index, int n, boolean allIndexIterators, Object arg)	Creates an interval iterator suitable for this AbstractIntervalDocumentIterator.
IntervalIterator	intervalIterator()	Returns the interval iterator of this document iterator for single-index queries.
IntervalIterator	intervalIterator(Index index)	Returns the interval iterator of this document iterator for the given index.
Reference2ReferenceMap<Index,IntervalIterator>	intervalIterators()	Returns an unmodifiable map from indices to interval iterators.
boolean	mayHaveNext()	Returns whether there may be a next document, possibly with false positives.
long	nextDocument()	Returns the next document provided by this document iterator, or DocumentIterator.END_OF_LIST if no more documents are available.
long	skipTo(long n)	Skips all documents smaller than n.
String	toString()

Methods inherited from class it.unimi.di.big.mg4j.search.AbstractIntervalDocumentIterator

allIndexIterators, indices, indices

Methods inherited from class it.unimi.di.big.mg4j.search.AbstractDocumentIterator

document, ensureOnADocument, weight, weight

Methods inherited from class java.lang.Object

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

Field Detail

documentIterator

protected final DocumentIterator documentIterator

The underlying iterator.

threshold

protected final int threshold

The iterator threshold.

Constructor Detail

LowPassDocumentIterator

protected LowPassDocumentIterator(DocumentIterator documentIterator,
                                  int threshold)

Creates a new low-pass document iterator over a given iterator.

Parameters:

documentIterator - the iterator to be filtered.

threshold - the filter threshold.

Method Detail

getInstance

public static LowPassDocumentIterator getInstance(DocumentIterator it,
                                                  int threshold)

Returns a low-pass document iterator over a given iterator.

Parameters:

it - the iterator to be filtered.

threshold - the filter threshold.

getIntervalIterator

protected IntervalIterator getIntervalIterator(Index index,
                                               int n,
                                               boolean allIndexIterators,
                                               Object arg)

Description copied from class: AbstractIntervalDocumentIterator

Creates an interval iterator suitable for this AbstractIntervalDocumentIterator.

Specified by:

getIntervalIterator in class AbstractIntervalDocumentIterator

Parameters:

index - the reference index for the iterator, or null.

n - the number of underlying or component iterators.

allIndexIterators - whether all underlying or component iterators are index iterators.

arg - an optional argument.

Returns:

an interval iterator suitable for this AbstractIntervalDocumentIterator.

nextDocument

public long nextDocument()
                  throws IOException

Description copied from interface: DocumentIterator

Returns the next document provided by this document iterator, or DocumentIterator.END_OF_LIST if no more documents are available.

Returns:

the next document, or DocumentIterator.END_OF_LIST if no more documents are available.

Throws:

IOException

mayHaveNext

public boolean mayHaveNext()

Description copied from interface: DocumentIterator

Returns whether there may be a next document, possibly with false positives.

Specified by:

mayHaveNext in interface DocumentIterator

Overrides:

mayHaveNext in class AbstractDocumentIterator

Returns:

true there may be a next document; false if certainly there is no next document.

skipTo

public long skipTo(long n)
            throws IOException

Description copied from interface: DocumentIterator

Skips all documents smaller than n.

Define the current document k associated with this document iterator as follows:

• -1, if DocumentIterator.nextDocument() and this method have never been called;
• DocumentIterator.END_OF_LIST, if a call to this method or to DocumentIterator.nextDocument() returned DocumentIterator.END_OF_LIST;
• the last value returned by a call to DocumentIterator.nextDocument() or this method, otherwise.

If k is larger than or equal to n, then this method does nothing and returns k. Otherwise, a call to this method is equivalent to

 while( ( k = nextDocument() ) < n );
 return k;
 

Thus, when a result k ≠ DocumentIterator.END_OF_LIST is returned, the state of this iterator will be exactly the same as after a call to DocumentIterator.nextDocument() that returned k. In particular, the first document larger than or equal to n (when returned by this method) will not be returned by the next call to DocumentIterator.nextDocument().

Parameters:

n - a document pointer.

Returns:

a document pointer larger than or equal to n if available, DocumentIterator.END_OF_LIST otherwise.

Throws:

IOException

intervalIterators

public Reference2ReferenceMap<Index,IntervalIterator> intervalIterators()
                                                                       throws IOException

Description copied from interface: DocumentIterator

Returns an unmodifiable map from indices to interval iterators.

After a call to DocumentIterator.nextDocument(), this map can be used to retrieve the intervals in the current document. An invocation of Map.get(java.lang.Object) on this map with argument index yields the same result as intervalIterator(index).

Returns:

a map from indices to interval iterators over the current document.

Throws:

IOException

See Also:

DocumentIterator.intervalIterator(Index)

intervalIterator

public IntervalIterator intervalIterator()
                                  throws IOException

Description copied from interface: DocumentIterator

Returns the interval iterator of this document iterator for single-index queries.

This is a commodity method that can be used only for queries built over a single index.

Returns:

an interval iterator.

Throws:

IOException

See Also:

DocumentIterator.intervalIterator(Index)

intervalIterator

public IntervalIterator intervalIterator(Index index)
                                  throws IOException

Description copied from interface: DocumentIterator

Returns the interval iterator of this document iterator for the given index.

After a call to DocumentIterator.nextDocument(), this iterator can be used to retrieve the intervals in the current document (the one returned by DocumentIterator.nextDocument()) for the index index.

Note that if all indices have positions, it is guaranteed that at least one index will return an interval. However, for disjunctive queries it cannot be guaranteed that all indices will return an interval.

Indices without positions always return IntervalIterators.TRUE. Thus, in presence of indices without positions it is possible that no intervals at all are available.

Parameters:

index - an index (must be one over which the query was built).

Returns:

an interval iterator over the current document in index.

Throws:

IOException

dispose

public void dispose()
             throws IOException

Description copied from interface: DocumentIterator

Disposes this document iterator, releasing all resources.

This method should propagate down to the underlying index iterators, where it should release resources such as open files and network connections. If you're doing your own resource tracking and pooling, then you do not need to call this method.

Throws:

IOException

accept

public <T> T accept(DocumentIteratorVisitor<T> visitor)
             throws IOException

Description copied from interface: DocumentIterator

Accepts a visitor.

A document iterator is usually structured as composite, with operators as internal nodes and IndexIterators as leaves. This method implements the visitor pattern.

Parameters:

visitor - the visitor.

Returns:

an object resulting from the visit, or null if the visit was interrupted.

Throws:

IOException

acceptOnTruePaths

public <T> T acceptOnTruePaths(DocumentIteratorVisitor<T> visitor)
                        throws IOException

Description copied from interface: DocumentIterator

Accepts a visitor after a call to DocumentIterator.nextDocument(), limiting recursion to true paths.

After a call to DocumentIterator.nextDocument(), a document iterator is positioned over a document. This call is equivalent to DocumentIterator.accept(DocumentIteratorVisitor), but visits only along true paths.

We define a true path as a path from the root of the composite that passes only through nodes whose associated subtree is positioned on the same document of the root. Note that OrDocumentIterators detach exhausted iterators from the composite tree, so true paths define the subtree that is causing the current document to satisfy the query represented by this document iterator.

For more elaboration, and the main application of this method, see CounterCollectionVisitor.

Parameters:

visitor - the visitor.

Returns:

an object resulting from the visit, or null if the visit was interrupted.

Throws:

IOException

See Also:

DocumentIterator.accept(DocumentIteratorVisitor), CounterCollectionVisitor

toString

public String toString()

Overrides:

toString in class Object