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java.lang.Objectit.unimi.dsi.fastutil.ints.AbstractIntIterator
it.unimi.dsi.mg4j.search.AbstractDocumentIterator
it.unimi.dsi.mg4j.search.DifferenceDocumentIterator
public class DifferenceDocumentIterator
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 all intervals that contain some interval of the second operand. 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 enlargment—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]).
Nested Class Summary |
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Nested classes/interfaces inherited from class it.unimi.dsi.mg4j.search.AbstractDocumentIterator |
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AbstractDocumentIterator.AbstractIntervalIterator |
Field Summary |
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Fields inherited from class it.unimi.dsi.mg4j.search.AbstractDocumentIterator |
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last, next |
Constructor Summary | |
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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 | |
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boolean |
accept(DocumentIteratorVisitor visitor)
Accepts a visitor. |
boolean |
acceptOnTruePaths(DocumentIteratorVisitor 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. |
int |
nextDocument()
Returns the next document provided by this document iterator, or -1 if no more documents are available. |
int |
skipTo(int n)
Skips all documents smaller than n . |
String |
toString()
|
Methods inherited from class it.unimi.dsi.mg4j.search.AbstractDocumentIterator |
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document, hasNext, iterator, nextInt |
Methods inherited from class it.unimi.dsi.fastutil.ints.AbstractIntIterator |
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next, remove, skip |
Methods inherited from class java.lang.Object |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Methods inherited from interface it.unimi.dsi.mg4j.search.DocumentIterator |
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document, iterator, nextInt |
Methods inherited from interface it.unimi.dsi.fastutil.ints.IntIterator |
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skip |
Methods inherited from interface java.util.Iterator |
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hasNext, next, remove |
Constructor Detail |
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protected DifferenceDocumentIterator(DocumentIterator minuendIterator, DocumentIterator subtrahendIterator, int leftMargin, int rightMargin)
minuendIterator
- the minuend.subtrahendIterator
- the subtrahend.Method Detail |
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public static DocumentIterator getInstance(DocumentIterator minuendIterator, DocumentIterator subtrahendIterator)
minuendIterator
- the minuend.subtrahendIterator
- the subtrahend.public static DocumentIterator getInstance(DocumentIterator minuendIterator, DocumentIterator subtrahendIterator, int leftMargin, int rightMargin)
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.public ReferenceSet<Index> indices()
DocumentIterator
indices
in interface DocumentIterator
public int nextDocument() throws IOException
DocumentIterator
Warning: the specification of this method has significantly changed as of MG4J 1.2.
The special return value -1 is used to mark the end of iteration (a NoSuchElementException
would have been thrown before in that case, so ho harm should be caused by this change). The reason
for this change is providing fully lazy iteration over documents. Fully lazy iteration
does not provide an hasNext()
method—you have to actually ask for the next
element and check the return value. Fully lazy iteration is much lighter on method calls (half) and
in most (if not all) MG4J classes leads to a much simpler logic. Moreover, DocumentIterator.nextDocument()
can be specified as throwing an IOException
, which avoids the pernicious proliferation
of try/catch blocks in very short, low-level methods (it was having a detectable impact on performance).
nextDocument
in interface DocumentIterator
IOException
public int skipTo(int n) throws IOException
DocumentIterator
n
.
Define the current document k
associated with this document iterator
as follows:
DocumentIterator.nextDocument()
and this method have never been called;
Integer.MAX_VALUE
, if a call to this method returned Integer.MAX_VALUE
;
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 ? Integer.MAX_VALUE : k;
Thus, when a result k
≠ Integer.MAX_VALUE
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()
.
skipTo
in interface DocumentIterator
n
- a document pointer.
n
if available, Integer.MAX_VALUE
otherwise.
IOException
public Reference2ReferenceMap<Index,IntervalIterator> intervalIterators() throws IOException
DocumentIterator
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)
.
intervalIterators
in interface DocumentIterator
IOException
DocumentIterator.intervalIterator(Index)
public IntervalIterator intervalIterator() throws IOException
DocumentIterator
This is a commodity method that can be used only for queries built over a single index.
intervalIterator
in interface DocumentIterator
IOException
DocumentIterator.intervalIterator(Index)
public IntervalIterator intervalIterator(Index index) throws IOException
DocumentIterator
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.
intervalIterator
in interface DocumentIterator
index
- an index (must be one over which the query was built).
index
.
IOException
public void dispose() throws IOException
DocumentIterator
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.
dispose
in interface DocumentIterator
IOException
public boolean accept(DocumentIteratorVisitor visitor) throws IOException
DocumentIterator
A document iterator is usually structured as composite,
with operators as internal nodes and IndexIterator
s
as leaves. This method implements the visitor pattern.
accept
in interface DocumentIterator
visitor
- the visitor.
IOException
public boolean acceptOnTruePaths(DocumentIteratorVisitor visitor) throws IOException
DocumentIterator
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 OrDocumentIterator
s
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
.
acceptOnTruePaths
in interface DocumentIterator
visitor
- the visitor.
IOException
DocumentIterator.accept(DocumentIteratorVisitor)
,
CounterCollectionVisitor
public String toString()
toString
in class Object
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