org.apache.lucene.util.fst.package.html Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of aem-sdk-api Show documentation

The Adobe Experience Manager SDK

There is a newer version: 2024.11.18751.20241128T090041Z-241100





   


Finite state transducers

This package implements 
Finite State Transducers with the following characteristics:

   Fast and low memory overhead construction of the minimal FST 
       (but inputs must be provided in sorted order)
   Low object overhead and quick deserialization (byte[] representation)
   Optional two-pass compression: {@link org.apache.lucene.util.fst.FST#pack FST.pack()}
   {@link org.apache.lucene.util.fst.Util#getByOutput Lookup-by-output} when the 
       outputs are in sorted order (e.g., ordinals or file pointers)
   Pluggable {@link org.apache.lucene.util.fst.Outputs Outputs} representation
   {@link org.apache.lucene.util.fst.Util#shortestPaths N-shortest-paths} search by
       weight
   Enumerators ({@link org.apache.lucene.util.fst.IntsRefFSTEnum IntsRef} and {@link org.apache.lucene.util.fst.BytesRefFSTEnum BytesRef}) that behave like {@link java.util.SortedMap SortedMap} iterators


FST Construction example:
    // Input values (keys). These must be provided to Builder in Unicode sorted order!
    String inputValues[] = {"cat", "dog", "dogs"};
    long outputValues[] = {5, 7, 12};
    
    PositiveIntOutputs outputs = PositiveIntOutputs.getSingleton();
    Builder<Long> builder = new Builder<Long>(INPUT_TYPE.BYTE1, outputs);
    BytesRef scratchBytes = new BytesRef();
    IntsRef scratchInts = new IntsRef();
    for (int i = 0; i < inputValues.length; i++) {
      scratchBytes.copyChars(inputValues[i]);
      builder.add(Util.toIntsRef(scratchBytes, scratchInts), outputValues[i]);
    }
    FST<Long> fst = builder.finish();

Retrieval by key:
    Long value = Util.get(fst, new BytesRef("dog"));
    System.out.println(value); // 7

Retrieval by value:
    // Only works because outputs are also in sorted order
    IntsRef key = Util.getByOutput(fst, 12);
    System.out.println(Util.toBytesRef(key, scratchBytes).utf8ToString()); // dogs

Iterate over key-value pairs in sorted order:
    // Like TermsEnum, this also supports seeking (advance)
    BytesRefFSTEnum<Long> iterator = new BytesRefFSTEnum<Long>(fst);
    while (iterator.next() != null) {
      InputOutput<Long> mapEntry = iterator.current();
      System.out.println(mapEntry.input.utf8ToString());
      System.out.println(mapEntry.output);
    }

N-shortest paths by weight:
    Comparator<Long> comparator = new Comparator<Long>() {
      public int compare(Long left, Long right) {
        return left.compareTo(right);
      }
    };
    Arc<Long> firstArc = fst.getFirstArc(new Arc<Long>());
    MinResult<Long> paths[] = Util.shortestPaths(fst, firstArc, comparator, 2);
    System.out.println(Util.toBytesRef(paths[0].input, scratchBytes).utf8ToString()); // cat
    System.out.println(paths[0].output); // 5
    System.out.println(Util.toBytesRef(paths[1].input, scratchBytes).utf8ToString()); // dog
    System.out.println(paths[1].output); // 7