org.apache.lucene.util.fst.package-info Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
* 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();
* IntsRefBuilder scratchInts = new IntsRefBuilder();
* 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
*
*/
package org.apache.lucene.util.fst;