Package org.apache.lucene.search.suggest.analyzing

# Class FuzzySuggester

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

All Implemented Interfaces:
  `Accountable`

public final class FuzzySuggester extends AnalyzingSuggester
Implements a fuzzy `AnalyzingSuggester`. The similarity measurement is based on the Damerau-Levenshtein (optimal string alignment) algorithm, though you can explicitly choose classic Levenshtein by passing `false` for the `transpositions` parameter.

At most, this query will match terms up to 2 edits. Higher distances are not supported. Note that the fuzzy distance is measured in "byte space" on the bytes returned by the `TokenStream`'s `TermToBytesRefAttribute`, usually UTF8. By default the analyzed bytes must be at least 3 `DEFAULT_MIN_FUZZY_LENGTH` bytes before any edits are considered. Furthermore, the first 1 `DEFAULT_NON_FUZZY_PREFIX` byte is not allowed to be edited. We allow up to 1 (@link #DEFAULT_MAX_EDITS} edit. If `unicodeAware` parameter in the constructor is set to true, maxEdits, minFuzzyLength, transpositions and nonFuzzyPrefix are measured in Unicode code points (actual letters) instead of bytes.

NOTE: This suggester does not boost suggestions that required no edits over suggestions that did require edits. This is a known limitation.

Note: complex query analyzers can have a significant impact on the lookup performance. It's recommended to not use analyzers that drop or inject terms like synonyms to keep the complexity of the prefix intersection low for good lookup performance. At index time, complex analyzers can safely be used.

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

Fields
Modifier and Type
Field
Description
`static final int`
`DEFAULT_MAX_EDITS`
The default maximum number of edits for fuzzy suggestions.
`static final int`
`DEFAULT_MIN_FUZZY_LENGTH`
The default minimum length of the key passed to `AnalyzingSuggester.lookup(java.lang.CharSequence, java.util.Set<org.apache.lucene.util.BytesRef>, boolean, int)` before any edits are allowed.
`static final int`
`DEFAULT_NON_FUZZY_PREFIX`
The default prefix length where edits are not allowed.
`static final boolean`
`DEFAULT_TRANSPOSITIONS`
The default transposition value passed to `LevenshteinAutomata`
`static final boolean`
`DEFAULT_UNICODE_AWARE`
Measure maxEdits, minFuzzyLength, transpositions and nonFuzzyPrefix parameters in Unicode code points (actual letters) instead of bytes.

### Fields inherited from class org.apache.lucene.search.suggest.analyzing.AnalyzingSuggester

`EXACT_FIRST, PRESERVE_SEP`

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

`CHARSEQUENCE_COMPARATOR`

### Fields inherited from interface org.apache.lucene.util.Accountable

`NULL_ACCOUNTABLE`

## Constructor Summary

Constructors
Constructor
Description
`FuzzySuggester(Directory tempDir, String tempFileNamePrefix, Analyzer analyzer)`
Creates a `FuzzySuggester` instance initialized with default values.
`FuzzySuggester(Directory tempDir, String tempFileNamePrefix, Analyzer indexAnalyzer, Analyzer queryAnalyzer)`
Creates a `FuzzySuggester` instance with an index and query analyzer initialized with default values.
`FuzzySuggester(Directory tempDir, String tempFileNamePrefix, Analyzer indexAnalyzer, Analyzer queryAnalyzer, int options, int maxSurfaceFormsPerAnalyzedForm, int maxGraphExpansions, boolean preservePositionIncrements, int maxEdits, boolean transpositions, int nonFuzzyPrefix, int minFuzzyLength, boolean unicodeAware)`
Creates a `FuzzySuggester` instance.

## Method Summary

Modifier and Type
Method
Description
`protected Automaton`
`convertAutomaton(Automaton a)`
Used by subclass to change the lookup automaton, if necessary.
`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.

### Methods inherited from class org.apache.lucene.search.suggest.analyzing.AnalyzingSuggester

`build, get, getChildResources, getCount, load, lookup, ramBytesUsed, store`

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

`build, load, lookup, lookup, store`

### Methods inherited from class java.lang.Object

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

## Field Details

### DEFAULT_UNICODE_AWARE

public static final boolean DEFAULT_UNICODE_AWARE
Measure maxEdits, minFuzzyLength, transpositions and nonFuzzyPrefix parameters in Unicode code points (actual letters) instead of bytes.

See Also:
  - Constant Field Values

### DEFAULT_MIN_FUZZY_LENGTH

public static final int DEFAULT_MIN_FUZZY_LENGTH
The default minimum length of the key passed to `AnalyzingSuggester.lookup(java.lang.CharSequence, java.util.Set<org.apache.lucene.util.BytesRef>, boolean, int)` before any edits are allowed.

See Also:
  - Constant Field Values

### DEFAULT_NON_FUZZY_PREFIX

public static final int DEFAULT_NON_FUZZY_PREFIX
The default prefix length where edits are not allowed.

See Also:
  - Constant Field Values

### DEFAULT_MAX_EDITS

public static final int DEFAULT_MAX_EDITS
The default maximum number of edits for fuzzy suggestions.

See Also:
  - Constant Field Values

### DEFAULT_TRANSPOSITIONS

public static final boolean DEFAULT_TRANSPOSITIONS
The default transposition value passed to `LevenshteinAutomata`

See Also:
  - Constant Field Values

## Constructor Details

### FuzzySuggester

public FuzzySuggester(Directory tempDir, String tempFileNamePrefix, Analyzer analyzer)
Creates a `FuzzySuggester` instance initialized with default values.

Parameters:
  `analyzer` - the analyzer used for this suggester

### FuzzySuggester

public FuzzySuggester(Directory tempDir, String tempFileNamePrefix, Analyzer indexAnalyzer, Analyzer queryAnalyzer)
Creates a `FuzzySuggester` instance with an index and query analyzer initialized with default values.

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

### FuzzySuggester

public FuzzySuggester(Directory tempDir, String tempFileNamePrefix, Analyzer indexAnalyzer, Analyzer queryAnalyzer, int options, int maxSurfaceFormsPerAnalyzedForm, int maxGraphExpansions, boolean preservePositionIncrements, int maxEdits, boolean transpositions, int nonFuzzyPrefix, int minFuzzyLength, boolean unicodeAware)
Creates a `FuzzySuggester` instance.

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 `AnalyzingSuggester.EXACT_FIRST`, `AnalyzingSuggester.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 automaton
  `maxEdits` - must be >= 0 and <= `LevenshteinAutomata.MAXIMUM_SUPPORTED_DISTANCE` .
  `transpositions` - `true` if transpositions should be treated as a primitive edit operation. If this is false, comparisons will implement the classic Levenshtein algorithm.
  `nonFuzzyPrefix` - length of common (non-fuzzy) prefix (see default `DEFAULT_NON_FUZZY_PREFIX`
  `minFuzzyLength` - minimum length of lookup key before any edits are allowed (see default `DEFAULT_MIN_FUZZY_LENGTH`)
  `unicodeAware` - operate Unicode code points instead of bytes.

## Method Details

### 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
Description copied from class: `AnalyzingSuggester`
Returns all prefix paths to initialize the search.

Overrides:
  `getFullPrefixPaths` in class `AnalyzingSuggester`
Throws:
  `IOException`

### convertAutomaton

protected Automaton convertAutomaton(Automaton a)
Description copied from class: `AnalyzingSuggester`
Used by subclass to change the lookup automaton, if necessary.

Overrides:
  `convertAutomaton` in class `AnalyzingSuggester`