it.unimi.di.mg4j.search
Class RemappingDocumentIterator

java.lang.Object
  extended by it.unimi.di.mg4j.search.RemappingDocumentIterator
All Implemented Interfaces:
DocumentIterator

public class RemappingDocumentIterator
extends Object
implements DocumentIterator

A decorator that remaps interval iterator requests.

Sometimes it is necessary to combine with positional operators (e.g., ConsecutiveDocumentIterator) intervals from different indices. By wrapping with an instance of this class a DocumentIterator, the requests for intervals will be remapped following a map given at construction time.

This class distinguishes between internal indices, which are those actually provided by the underlying DocumentIterator, and external indices, which are those exposed by indices(), and with which intervalIterator(Index) should be called. The map provided at construction time should remap external indices to internal indices (note the inversion w.r.t. Remap). In many cases, a singleton map will be appropriate.

Since:
2.2
Author:
Sebastiano Vigna

Field Summary
 
Fields inherited from interface it.unimi.di.mg4j.search.DocumentIterator
END_OF_LIST
 
Constructor Summary
RemappingDocumentIterator(DocumentIterator documentIterator, Reference2ReferenceMap<? extends Index,? extends Index> indexInverseRemapping)
          Creates a new remapping document iterator wrapping a given document iterator and remapping interval-iterator requests through a given mapping from external to internal indices.
 
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.
 int document()
          Returns the last document returned by DocumentIterator.nextDocument().
 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()
           
 boolean mayHaveNext()
          Returns whether there may be a next document, possibly with false positives.
 int nextDocument()
          Returns the next document provided by this document iterator, or DocumentIterator.END_OF_LIST if no more documents are available.
 int skipTo(int n)
          Skips all documents smaller than n.
 String toString()
           
 double weight()
          Returns the weight associated with this iterator.
 DocumentIterator weight(double weight)
          Sets the weight of this index iterator.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Constructor Detail

RemappingDocumentIterator

public RemappingDocumentIterator(DocumentIterator documentIterator,
                                 Reference2ReferenceMap<? extends Index,? extends Index> indexInverseRemapping)
Creates a new remapping document iterator wrapping a given document iterator and remapping interval-iterator requests through a given mapping from external to internal indices.

Parameters:
documentIterator - the underlying document iterator.
indexInverseRemapping - the mapping from external to internal indices.
Method Detail

document

public int document()
Description copied from interface: DocumentIterator
Returns the last document returned by DocumentIterator.nextDocument().

Specified by:
document in interface DocumentIterator
Returns:
the last document returned by DocumentIterator.nextDocument(), -1 if no document has been returned yet, and DocumentIterator.END_OF_LIST if the list of results has been exhausted.

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.

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

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)

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)

nextDocument

public int 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.

Specified by:
nextDocument in interface DocumentIterator
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
Returns:
true there may be a next document; false if certainly there is no next document.

skipTo

public int skipTo(int 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:

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 kDocumentIterator.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

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

iterator

public IntervalIterator iterator()

weight

public double weight()
Description copied from interface: DocumentIterator
Returns the weight associated with this iterator.

The number returned by this method has no fixed semantics: different scorers might choose different interpretations, or even ignore it.

Specified by:
weight in interface DocumentIterator
Returns:
the weight associated with this iterator.

weight

public DocumentIterator weight(double weight)
Description copied from interface: DocumentIterator
Sets the weight of this index iterator.

Specified by:
weight in interface DocumentIterator
Parameters:
weight - the weight of this index iterator.
Returns:
this document iterator.

toString

public String toString()
Overrides:
toString in class Object