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java.lang.Objectit.unimi.dsi.fastutil.ints.AbstractIntIterator
it.unimi.dsi.mg4j.search.CachingDocumentIterator
public class CachingDocumentIterator
A decorator that caches the intervals produced by the underlying document iterator.
Often, scores exhaust the intervals produced by a document iterator to compute their
result. However, often you also need those intervals for other purposes (maybe just
because you are aggregating several interval-based scorers). Decorating a document
iterator with an instance of this class you get again a document iterator, but its intervals can
be retrieved several times by calling intervalIterator(Index)
, intervalIterator()
and
intervalIterators()
.
Important: calls are not nestable: when you require again an iterator,
the one previously returned is no longer valid, and when the current document changes (e.g.,
because of a call to nextDocument()
) the previously returned interval iterators are invalidated.
Constructor Summary | |
---|---|
CachingDocumentIterator(DocumentIterator documentIterator)
|
Method Summary | ||
---|---|---|
|
accept(DocumentIteratorVisitor<T> visitor)
Accepts a visitor. |
|
|
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. |
|
int |
document()
Returns the last document returned by DocumentIterator.nextDocument() . |
|
boolean |
hasNext()
|
|
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. |
|
IntervalIterator |
iterator()
An alias for DocumentIterator.intervalIterator() , that has the same limitations (i.e., it will work only if
there is just one index), and that catches IOException s. |
|
int |
nextDocument()
Returns the next document provided by this document iterator, or -1 if no more documents are available. |
|
int |
nextInt()
Returns the next document. |
|
int |
skipTo(int n)
Skips all documents smaller than n . |
|
double |
weight()
Returns the weight associated to this iterator. |
|
DocumentIterator |
weight(double weight)
Sets the weight of this index iterator. |
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, toString, wait, wait, wait |
Methods inherited from interface it.unimi.dsi.fastutil.ints.IntIterator |
---|
skip |
Methods inherited from interface java.util.Iterator |
---|
next, remove |
Constructor Detail |
---|
public CachingDocumentIterator(DocumentIterator documentIterator)
Method Detail |
---|
public int document()
DocumentIterator
DocumentIterator.nextDocument()
.
document
in interface DocumentIterator
DocumentIterator.nextDocument()
, or -1 if no document has been returned yet.public boolean hasNext()
hasNext
in interface Iterator<Integer>
public ReferenceSet<Index> indices()
DocumentIterator
indices
in interface DocumentIterator
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 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 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 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 nextInt()
DocumentIterator
nextInt
in interface IntIterator
nextInt
in interface DocumentIterator
nextInt
in class AbstractIntIterator
DocumentIterator.nextDocument()
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 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 <T> T accept(DocumentIteratorVisitor<T> 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.
null
if the visit was interrupted.
IOException
public <T> T acceptOnTruePaths(DocumentIteratorVisitor<T> 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.
null
if the visit was interrupted.
IOException
DocumentIterator.accept(DocumentIteratorVisitor)
,
CounterCollectionVisitor
public IntervalIterator iterator()
DocumentIterator
DocumentIterator.intervalIterator()
, that has the same limitations (i.e., it will work only if
there is just one index), and that catches IOException
s.
iterator
in interface DocumentIterator
iterator
in interface Iterable<Interval>
public double weight()
DocumentIterator
The number returned by this method has no fixed semantics: different scorers might choose different interpretations, or even ignore it.
weight
in interface DocumentIterator
public DocumentIterator weight(double weight)
DocumentIterator
weight
in interface DocumentIterator
weight
- the weight of this index iterator.
|
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