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java.lang.Objectit.unimi.dsi.fastutil.ints.AbstractIntIterator
it.unimi.dsi.mg4j.search.AbstractDocumentIterator
it.unimi.dsi.mg4j.search.AlignDocumentIterator
public class AlignDocumentIterator
A document iterator that aligns the results of a number of document iterators over different indices.
This class is an example of cross-index computation. As in the case of an
AndDocumentIterator
, we intersect the posting lists. However, once
we get to the index level, we actually return just intervals that appear in
all component iterators. Of course, this is meaningful only if all
indices represent different views on the same data, a typical example being
semantic tagging.
An instance of this class exposes a single interval iterator associated to
the index of the first component iterator, as all interval iterators
are exhausted during the computation of their intersection.
Correspondingly, a call to IntervalIterator.intervalTerms(IntSet)
just
returns the terms related to the first component iterator.
Nested Class Summary |
---|
Nested classes/interfaces inherited from class it.unimi.dsi.mg4j.search.AbstractDocumentIterator |
---|
AbstractDocumentIterator.AbstractIntervalIterator |
Field Summary |
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Fields inherited from class it.unimi.dsi.mg4j.search.AbstractDocumentIterator |
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last, next, weight |
Constructor Summary | |
---|---|
protected |
AlignDocumentIterator(DocumentIterator aligneeIterator,
DocumentIterator alignerIterator)
|
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. |
|
static DocumentIterator |
getInstance(DocumentIterator aligneeIterator,
DocumentIterator alignerIterator)
Returns a document iterator that aligns the first iterator to the second. |
|
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 . |
Methods inherited from class it.unimi.dsi.mg4j.search.AbstractDocumentIterator |
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document, hasNext, iterator, nextInt, 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, toString, wait, wait, wait |
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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next, remove |
Constructor Detail |
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protected AlignDocumentIterator(DocumentIterator aligneeIterator, DocumentIterator alignerIterator)
Method Detail |
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public static DocumentIterator getInstance(DocumentIterator aligneeIterator, DocumentIterator alignerIterator)
aligneeIterator
- the iterator to be aligned.alignerIterator
- the iterator used to align aligneeIterator
.
aligneeIterator
on alignerIterator
.public ReferenceSet<Index> indices()
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).
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()
.
n
- a document pointer.
n
if available, Integer.MAX_VALUE
otherwise.
IOException
public IntervalIterator intervalIterator() throws IOException
DocumentIterator
This is a commodity method that can be used only for queries built over a single index.
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)
.
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.
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.
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.
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
.
visitor
- the visitor.
null
if the visit was interrupted.
IOException
DocumentIterator.accept(DocumentIteratorVisitor)
,
CounterCollectionVisitor
|
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