content: /*
   * 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.
   */
  package org.apache.arrow.algorithm.dictionary;
  
  import org.apache.arrow.algorithm.search.VectorSearcher;
  import org.apache.arrow.algorithm.sort.VectorValueComparator;
  import org.apache.arrow.vector.BaseIntVector;
  import org.apache.arrow.vector.ValueVector;
  
  /**
   * Dictionary encoder based on searching.
   *
   * @param <E> encoded vector type.
   * @param <D> decoded vector type, which is also the dictionary type.
   */
  public class SearchDictionaryEncoder<E extends BaseIntVector, D extends ValueVector>
      implements DictionaryEncoder<E, D> {
  
    /** The dictionary for encoding/decoding. It must be sorted. */
    private final D dictionary;
  
    /** The criteria by which the dictionary is sorted. */
    private final VectorValueComparator<D> comparator;
  
    /** A flag indicating if null should be encoded. */
    private final boolean encodeNull;
  
    /**
     * Constructs a dictionary encoder.
     *
     * @param dictionary the dictionary. It must be in sorted order.
     * @param comparator the criteria for sorting.
     */
    public SearchDictionaryEncoder(D dictionary, VectorValueComparator<D> comparator) {
      this(dictionary, comparator, false);
    }
  
    /**
     * Constructs a dictionary encoder.
     *
     * @param dictionary the dictionary. It must be in sorted order.
     * @param comparator the criteria for sorting.
     * @param encodeNull a flag indicating if null should be encoded. It determines the behaviors for
     *     processing null values in the input during encoding. When a null is encountered in the
     *     input, 1) If the flag is set to true, the encoder searches for the value in the dictionary,
     *     and outputs the index in the dictionary. 2) If the flag is set to false, the encoder simply
     *     produces a null in the output.
     */
    public SearchDictionaryEncoder(
        D dictionary, VectorValueComparator<D> comparator, boolean encodeNull) {
      this.dictionary = dictionary;
      this.comparator = comparator;
      this.encodeNull = encodeNull;
    }
  
    /**
     * Encodes an input vector by binary search. So the algorithm takes O(n * log(m)) time, where n is
     * the length of the input vector, and m is the length of the dictionary.
     *
     * @param input the input vector.
     * @param output the output vector. Note that it must be in a fresh state. At least, all its
     *     validity bits should be clear.
     */
    @Override
    public void encode(D input, E output) {
      for (int i = 0; i < input.getValueCount(); i++) {
        if (!encodeNull && input.isNull(i)) {
          // for this case, we should simply output a null in the output.
          // by assuming the output vector is fresh, we do nothing here.
          continue;
        }
  
        int index = VectorSearcher.binarySearch(dictionary, comparator, input, i);
        if (index == -1) {
          throw new IllegalArgumentException("The data element is not found in the dictionary: " + i);
        }
        output.setWithPossibleTruncate(i, index);
      }
      output.setValueCount(input.getValueCount());
    }
  }
  