Package org.apache.lucene.search.suggest.fst

Class FSTCompletionLookup

java.lang.Object
org.apache.lucene.search.suggest.Lookup
org.apache.lucene.search.suggest.fst.FSTCompletionLookup
public class FSTCompletionLookup extends Lookup
An adapter from Lookup API to FSTCompletion.

This adapter differs from FSTCompletion in that it attempts to discretize any "weights" as passed from in InputIterator.weight() to match the number of buckets. For the rationale for bucketing, see FSTCompletion.

Note:Discretization requires an additional sorting pass.

The range of weights for bucketing/ discretization is determined by sorting the input by weight and then dividing into equal ranges. Then, scores within each range are assigned to that bucket.

Note that this means that even large differences in weights may be lost during automaton construction, but the overall distinction between "classes" of weights will be preserved regardless of the distribution of weights.

For fine-grained control over which weights are assigned to which buckets, use FSTCompletion directly or TSTLookup, for example.

See Also:

  • Constructor Details

    • FSTCompletionLookup

      public FSTCompletionLookup()
      This constructor prepares for creating a suggested FST using the build(InputIterator) method. The number of weight discretization buckets is set to FSTCompletion.DEFAULT_BUCKETS and exact matches are promoted to the top of the suggestions list.

    • FSTCompletionLookup

      public FSTCompletionLookup(int buckets, boolean exactMatchFirst)
      This constructor prepares for creating a suggested FST using the build(InputIterator) method.
      Parameters:
      buckets - The number of weight discretization buckets (see FSTCompletion for details).
      exactMatchFirst - If true exact matches are promoted to the top of the suggestions list. Otherwise they appear in the order of discretized weight and alphabetical within the bucket.

    • FSTCompletionLookup

      public FSTCompletionLookup(FSTCompletion completion, boolean exactMatchFirst)
      This constructor takes a pre-built automaton.
      Parameters:
      completion - An instance of FSTCompletion.
      exactMatchFirst - If true exact matches are promoted to the top of the suggestions list. Otherwise they appear in the order of discretized weight and alphabetical within the bucket.

  • Method Details

    • 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

    • lookup

      public List<Lookup.LookupResult> lookup(CharSequence key, boolean higherWeightsFirst, 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.
      higherWeightsFirst - 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)

    • get

      public Object get(CharSequence key)
      Returns the bucket (weight) as a Long for the provided key if it exists, otherwise null if it does not.

    • 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.

    • sizeInBytes

      public long sizeInBytes()
      Description copied from class: Lookup
      Get the size of the underlying lookup implementation in memory
      Specified by:
      sizeInBytes in class Lookup
      Returns:
      ram size of the lookup implementation in bytes

    • 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