it.unimi.dsi.mg4j.search
Class DifferenceDocumentIterator

java.lang.Object
  it.unimi.dsi.fastutil.ints.AbstractIntIterator
      it.unimi.dsi.mg4j.search.AbstractDocumentIterator
          it.unimi.dsi.mg4j.search.DifferenceDocumentIterator

All Implemented Interfaces:

IntIterator, DocumentIterator, Iterable<Interval>, Iterator<Integer>

public class DifferenceDocumentIterator
extends AbstractDocumentIterator
implements DocumentIterator

A document iterator that computes the Brouwerian difference between two given document iterators.

In the lattice of interval antichains, the Brouwerian difference is obtained by deleting from the first operand (the minuend) all intervals that contain some interval of the second operand (the subtrahend). Thus, Brouwerian difference can be fruitfully employed to kill intervals containing a term or, even more fruitfully, to change at query time the granularity of an index by subtracting from the results of a query those length-two intervals that cross the cutpoints between the desired parts of the index.

Additionally, this class provides interval enlargement—by using a suitable factory method each interval returned by the subtrahend will be enlarged to the left and to the right by the given amount (e.g., if the left margin is 1 and the right margin is 2 the interval [2..3] will turn into [1..5]).

Note that while accept(DocumentIteratorVisitor) will recursively visit both the minuend and the subtrahend, acceptOnTruePaths(DocumentIteratorVisitor) will visit only the minuend.

Since:

1.2

Author:

Sebastiano Vigna

Nested Class Summary

Nested classes/interfaces inherited from class it.unimi.dsi.mg4j.search.AbstractDocumentIterator

AbstractDocumentIterator.AbstractIntervalIterator

Field Summary

Fields inherited from class it.unimi.dsi.mg4j.search.AbstractDocumentIterator

ahead, curr, weight

Fields inherited from interface it.unimi.dsi.mg4j.search.DocumentIterator

END_OF_LIST

Constructor Summary

protected

DifferenceDocumentIterator(DocumentIterator minuendIterator, DocumentIterator subtrahendIterator, int leftMargin, int rightMargin) Creates a new difference document iterator given a minuend and a subtrahend iterator.

Method Summary

<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 DocumentIterator	getInstance(DocumentIterator minuendIterator, DocumentIterator subtrahendIterator) Returns new difference document iterator given a minuend and a subtrahend iterator.
static DocumentIterator	getInstance(DocumentIterator minuendIterator, DocumentIterator subtrahendIterator, int leftMargin, int rightMargin) Returns new difference document iterator given a minuend and a subtrahend iterator.
ReferenceSet<Index>	indices() Returns the set of indices over which this iterator is built.
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.
protected int	nextDocumentInternal()
int	skipTo(int n) Skips all documents smaller than n.
String	toString()

Methods inherited from class it.unimi.dsi.mg4j.search.AbstractDocumentIterator

document, ensureOnADocument, fromNextDocument, hasNext, iterator, nextDocument, nextInt, toNextDocument, weight, weight

Methods inherited from class it.unimi.dsi.fastutil.ints.AbstractIntIterator

next, remove, skip

Methods inherited from class java.lang.Object

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

Methods inherited from interface it.unimi.dsi.mg4j.search.DocumentIterator

document, iterator, nextDocument, nextInt, weight, weight

Methods inherited from interface it.unimi.dsi.fastutil.ints.IntIterator

skip

Methods inherited from interface java.util.Iterator

hasNext, next, remove

Constructor Detail

DifferenceDocumentIterator

protected DifferenceDocumentIterator(DocumentIterator minuendIterator,
                                     DocumentIterator subtrahendIterator,
                                     int leftMargin,
                                     int rightMargin)

Creates a new difference document iterator given a minuend and a subtrahend iterator.

Parameters:

minuendIterator - the minuend.

subtrahendIterator - the subtrahend.

Method Detail

getInstance

public static DocumentIterator getInstance(DocumentIterator minuendIterator,
                                           DocumentIterator subtrahendIterator)

Returns new difference document iterator given a minuend and a subtrahend iterator.

Parameters:

minuendIterator - the minuend.

subtrahendIterator - the subtrahend.

getInstance

public static DocumentIterator getInstance(DocumentIterator minuendIterator,
                                           DocumentIterator subtrahendIterator,
                                           int leftMargin,
                                           int rightMargin)

Returns new difference document iterator given a minuend and a subtrahend iterator.

Parameters:

minuendIterator - the minuend.

subtrahendIterator - the subtrahend.

leftMargin - a margin that will be added to the left of each interval.

rightMargin - a margin that will be added to the right of each interval.

indices

public ReferenceSet<Index> indices()

Description copied from interface: DocumentIterator

Returns the set of indices over which this iterator is built.

Specified by:

indices in interface DocumentIterator

Returns:

the set of indices over which this iterator is built.

nextDocumentInternal

protected int nextDocumentInternal()
                            throws IOException

Specified by:

nextDocumentInternal in class AbstractDocumentIterator

Throws:

IOException

skipTo

public int skipTo(int n)
           throws IOException

Description copied from interface: DocumentIterator

Skips all documents smaller than n. If Iterator.hasNext() has been called returning true but DocumentIterator.nextDocument() has not been called afterwards, then a call to DocumentIterator.skipTo(int) will be implicitly preceded by a call to DocumentIterator.nextDocument() (the only consequence is that skipping to the current document after a call to Iterator.hasNext() will return the next document).

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 returned DocumentIterator.END_OF_LIST, or DocumentIterator.nextDocument() returned -1;
• 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 && k != -1 );
 return k == -1 ? END_OF_LIST : 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().

Specified by:

skipTo in interface DocumentIterator

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).

Specified by:

intervalIterators in interface DocumentIterator

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.

Specified by:

intervalIterator in interface DocumentIterator

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.

Specified by:

intervalIterator in interface DocumentIterator

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.

Specified by:

dispose in interface DocumentIterator

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.

Specified by:

accept in interface DocumentIterator

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.

Specified by:

acceptOnTruePaths in interface DocumentIterator

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