org.apache.lucene.search.suggest.analyzing
Class AnalyzingSuggester

java.lang.Object
  org.apache.lucene.search.suggest.Lookup
      org.apache.lucene.search.suggest.analyzing.AnalyzingSuggester

Direct Known Subclasses:

FuzzySuggester

public class AnalyzingSuggester
extends Lookup

Suggester that first analyzes the surface form, adds the analyzed form to a weighted FST, and then does the same thing at lookup time. This means lookup is based on the analyzed form while suggestions are still the surface form(s).

This can result in powerful suggester functionality. For example, if you use an analyzer removing stop words, then the partial text "ghost chr..." could see the suggestion "The Ghost of Christmas Past". Note that position increments MUST NOT be preserved for this example to work, so you should call the constructor with preservePositionIncrements parameter set to false

If SynonymFilter is used to map wifi and wireless network to hotspot then the partial text "wirele..." could suggest "wifi router". Token normalization like stemmers, accent removal, etc., would allow suggestions to ignore such variations.

When two matching suggestions have the same weight, they are tie-broken by the analyzed form. If their analyzed form is the same then the order is undefined.

There are some limitations:

• A lookup from a query like "net" in English won't be any different than "net " (ie, user added a trailing space) because analyzers don't reflect when they've seen a token separator and when they haven't.
• If you're using StopFilter, and the user will type "fast apple", but so far all they've typed is "fast a", again because the analyzer doesn't convey whether it's seen a token separator after the "a", StopFilter will remove that "a" causing far more matches than you'd expect.
• Lookups with the empty string return no results instead of all results.

WARNING: This API is experimental and might change in incompatible ways in the next release.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.lucene.search.suggest.Lookup

Lookup.LookupPriorityQueue, Lookup.LookupResult

Field Summary

static int	EXACT_FIRST Include this flag in the options parameter to AnalyzingSuggester(Analyzer,Analyzer,int,int,int,boolean) to always return the exact match first, regardless of score.
static int	PRESERVE_SEP Include this flag in the options parameter to AnalyzingSuggester(Analyzer,Analyzer,int,int,int,boolean) to preserve token separators when matching.

Fields inherited from class org.apache.lucene.search.suggest.Lookup

CHARSEQUENCE_COMPARATOR

Constructor Summary

AnalyzingSuggester(Analyzer analyzer)
Calls AnalyzingSuggester(analyzer, analyzer, EXACT_FIRST | PRESERVE_SEP, 256, -1, true)

AnalyzingSuggester(Analyzer indexAnalyzer, Analyzer queryAnalyzer)
Calls AnalyzingSuggester(indexAnalyzer, queryAnalyzer, EXACT_FIRST | PRESERVE_SEP, 256, -1, true)

AnalyzingSuggester(Analyzer indexAnalyzer, Analyzer queryAnalyzer, int options, int maxSurfaceFormsPerAnalyzedForm, int maxGraphExpansions, boolean preservePositionIncrements)
Creates a new suggester.

Method Summary

void	build(InputIterator iterator) Builds up a new internal Lookup representation based on the given InputIterator.
protected Automaton	convertAutomaton(Automaton a) Used by subclass to change the lookup automaton, if necessary.
Object	get(CharSequence key) Returns the weight associated with an input string, or null if it does not exist.
long	getCount() Get the number of entries the lookup was built with
protected List<FSTUtil.Path<PairOutputs.Pair<Long,BytesRef>>>	getFullPrefixPaths(List<FSTUtil.Path<PairOutputs.Pair<Long,BytesRef>>> prefixPaths, Automaton lookupAutomaton, FST<PairOutputs.Pair<Long,BytesRef>> fst) Returns all prefix paths to initialize the search.
boolean	load(DataInput input) Discard current lookup data and load it from a previously saved copy.
List<Lookup.LookupResult>	lookup(CharSequence key, boolean onlyMorePopular, int num) Look up a key and return possible completion for this key.
long	sizeInBytes() Returns byte size of the underlying FST.
boolean	store(DataOutput output) Persist the constructed lookup data to a directory.

Methods inherited from class org.apache.lucene.search.suggest.Lookup

build, load, store

Methods inherited from class java.lang.Object

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

Field Detail

EXACT_FIRST

public static final int EXACT_FIRST

Include this flag in the options parameter to AnalyzingSuggester(Analyzer,Analyzer,int,int,int,boolean) to always return the exact match first, regardless of score. This has no performance impact but could result in low-quality suggestions.

See Also:

Constant Field Values

PRESERVE_SEP

public static final int PRESERVE_SEP

Include this flag in the options parameter to AnalyzingSuggester(Analyzer,Analyzer,int,int,int,boolean) to preserve token separators when matching.

See Also:

Constant Field Values

Constructor Detail

AnalyzingSuggester

public AnalyzingSuggester(Analyzer analyzer)

Calls AnalyzingSuggester(analyzer, analyzer, EXACT_FIRST | PRESERVE_SEP, 256, -1, true)

AnalyzingSuggester

public AnalyzingSuggester(Analyzer indexAnalyzer,
                          Analyzer queryAnalyzer)

Calls AnalyzingSuggester(indexAnalyzer, queryAnalyzer, EXACT_FIRST | PRESERVE_SEP, 256, -1, true)

AnalyzingSuggester

public AnalyzingSuggester(Analyzer indexAnalyzer,
                          Analyzer queryAnalyzer,
                          int options,
                          int maxSurfaceFormsPerAnalyzedForm,
                          int maxGraphExpansions,
                          boolean preservePositionIncrements)

Creates a new suggester.

Parameters:

indexAnalyzer - Analyzer that will be used for analyzing suggestions while building the index.

queryAnalyzer - Analyzer that will be used for analyzing query text during lookup

options - see EXACT_FIRST, PRESERVE_SEP

maxSurfaceFormsPerAnalyzedForm - Maximum number of surface forms to keep for a single analyzed form. When there are too many surface forms we discard the lowest weighted ones.

maxGraphExpansions - Maximum number of graph paths to expand from the analyzed form. Set this to -1 for no limit.

preservePositionIncrements - Whether position holes should appear in the automata

Method Detail

sizeInBytes

public long sizeInBytes()

Returns byte size of the underlying FST.

Specified by:

sizeInBytes in class Lookup

Returns:

ram size of the lookup implementation in bytes

convertAutomaton

protected Automaton convertAutomaton(Automaton a)

Used by subclass to change the lookup automaton, if necessary.

build

public void build(InputIterator iterator)
           throws IOException

Description copied from class: Lookup

Builds up a new internal Lookup representation based on the given InputIterator. The implementation might re-sort the data internally.

Specified by:

build in class Lookup

Throws:

IOException

store

public boolean store(DataOutput output)
              throws IOException

Description copied from class: Lookup

Persist the constructed lookup data to a directory. Optional operation.

Specified by:

store in class Lookup

Parameters:

output - DataOutput to write the data to.

Returns:

true if successful, false if unsuccessful or not supported.

Throws:

IOException - when fatal IO error occurs.

load

public boolean load(DataInput input)
             throws IOException

Description copied from class: Lookup

Discard current lookup data and load it from a previously saved copy. Optional operation.

Specified by:

load in class Lookup

Parameters:

input - the DataInput to load the lookup data.

Returns:

true if completed successfully, false if unsuccessful or not supported.

Throws:

IOException - when fatal IO error occurs.

lookup

public List<Lookup.LookupResult> lookup(CharSequence key,
                                        boolean onlyMorePopular,
                                        int num)

Description copied from class: Lookup

Look up a key and return possible completion for this key.

Specified by:

lookup in class Lookup

Parameters:

key - lookup key. Depending on the implementation this may be a prefix, misspelling, or even infix.

onlyMorePopular - return only more popular results

num - maximum number of results to return

Returns:

a list of possible completions, with their relative weight (e.g. popularity)

getCount

public long getCount()

Description copied from class: Lookup

Get the number of entries the lookup was built with

Specified by:

getCount in class Lookup

Returns:

total number of suggester entries

getFullPrefixPaths

protected List<FSTUtil.Path<PairOutputs.Pair<Long,BytesRef>>> getFullPrefixPaths(List<FSTUtil.Path<PairOutputs.Pair<Long,BytesRef>>> prefixPaths,
                                                                                 Automaton lookupAutomaton,
                                                                                 FST<PairOutputs.Pair<Long,BytesRef>> fst)
                                                                          throws IOException

Returns all prefix paths to initialize the search.

Throws:

IOException

get

public Object get(CharSequence key)

Returns the weight associated with an input string, or null if it does not exist.