org.terrier.realtime.multi

Class MultiLexicon

java.lang.Object

org.terrier.structures.Lexicon<String>

org.terrier.realtime.multi.MultiLexicon

All Implemented Interfaces:

Closeable, AutoCloseable, Iterable<Map.Entry<String,LexiconEntry>>

public class MultiLexicon
extends Lexicon<String>

A Lexicon index structure for use with a MultiIndex. It wraps around multiple lexicons from different index shards. IMPORTANT: Not all lexicon access methods are supported since a lexicon entry can appear in any number of lexicons! This has the following consequences:

• A MultiLexicon can not be iterated over without doing a temporary merge of all lexicon structures, hence we do not support this.
• getIthLexiconEntry() is not supported (the contents of the ith entry can change over time as new documents are added)
• The unique number of terms is not stored and needs to be calculated on-the-fly.

Properties

• MultiLexicon.approxNumEntries - do we try and approximate the number of lexicon entries (saves a lot of time but is inaccurate), default is true.

Since:

4.0

Author:

Richard McCreadie, Stuart Mackie

Constructor Summary

Constructors

Constructor and Description
MultiLexicon(Lexicon<String>[] lexicons, int[] numTerms) constructor.

Method Summary

Methods

Modifier and Type	Method and Description
void	close() Not implemented.
Lexicon<String>	getIthLexicon(int index)
Map.Entry<String,LexiconEntry>	getIthLexiconEntry(int index) This is an invalid method since a lexicon entry can appear in any number of lexicons.
Map.Entry<String,LexiconEntry>	getLexiconEntry(int termid) Get the term and LexiconEntry (contains statistics and a pointer) for a given term id.
Map.Entry<String,LexiconEntry>	getLexiconEntry(int termid, int shard) This is an extra lexicon entry method for fast lookups of LexiconEntry's by term id.
LexiconEntry	getLexiconEntry(String term) Get the LexiconEntry (contains statistics and a pointer) for the given term.
Iterator<Map.Entry<String,LexiconEntry>>	getLexiconEntryRange(String from, String to) Returns an iterator over a set of LexiconEntries within a range of entries in the lexicon.
Iterator<Map.Entry<String,LexiconEntry>>	iterator() Not implemented.
int	numberOfEntries() Return the number of entries in the lexicon

Methods inherited from class java.lang.Object

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

Constructor Detail

MultiLexicon

public MultiLexicon(Lexicon<String>[] lexicons,
            int[] numTerms)

constructor.

Method Detail

getIthLexicon

public Lexicon<String> getIthLexicon(int index)

numberOfEntries

public int numberOfEntries()

Return the number of entries in the lexicon

Specified by:

numberOfEntries in class Lexicon<String>

getLexiconEntry

public LexiconEntry getLexiconEntry(String term)

Get the LexiconEntry (contains statistics and a pointer) for the given term. Returns null if the term is not found in the lexicon.

Specified by:

getLexiconEntry in class Lexicon<String>

Parameters:

term - key to lookup the lexicon with

Returns:

LexiconEntry for that term, or null if not found

getLexiconEntry

public Map.Entry<String,LexiconEntry> getLexiconEntry(int termid)

Get the term and LexiconEntry (contains statistics and a pointer) for a given term id. Throws NoSuchElementException is the termid is not found.

Specified by:

getLexiconEntry in class Lexicon<String>

Parameters:

termid - the term id to lookup in the lexicon

Returns:

Map.Entry tuple containing the term and the LexiconEntry

getLexiconEntry

public Map.Entry<String,LexiconEntry> getLexiconEntry(int termid,
                                             int shard)

This is an extra lexicon entry method for fast lookups of LexiconEntry's by term id.

getIthLexiconEntry

public Map.Entry<String,LexiconEntry> getIthLexiconEntry(int index)

This is an invalid method since a lexicon entry can appear in any number of lexicons. In general DO NOT USE THIS! This method is only implemented such that a random term can be chosen within the JUnit tests.

Specified by:

getIthLexiconEntry in class Lexicon<String>

Parameters:

index - the entry number to lookup in the lexicon

Returns:

Map.Entry tuple containing the term and the LexiconEntry

iterator

public Iterator<Map.Entry<String,LexiconEntry>> iterator()

Not implemented.

close

public void close()
           throws IOException

Not implemented.

Throws:

IOException

getLexiconEntryRange

public Iterator<Map.Entry<String,LexiconEntry>> getLexiconEntryRange(String from,
                                                            String to)

Description copied from class: Lexicon

Returns an iterator over a set of LexiconEntries within a range of entries in the lexicon.

Specified by:

getLexiconEntryRange in class Lexicon<String>

Parameters:

from - low endpoint term in the subset, inclusive.

to - high endpoint term in the subset, exclusive.

Returns:

Iterator over the set.