samoa-instances/src/main/java/org/apache/samoa/instances/FilteredSparseInstanceData.java

/*
 * 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.samoa.instances;

/**
 * The Class FilteredSparseInstanceData.
 * <p>
 * This class is an extension to the original SparseInstanceData.
 * It has been created to be used with feature selection
 * algorithms for data streams.
 * In contrast to SparseInstanceData objects, missing values are
 * represented as NaNs instead of 0s (zeros).
 * This allows learners to skip features with missing values.
 *
 * @author Jean Paul Barddal
 */
public class FilteredSparseInstanceData extends SparseInstanceData {


  /**
   * Instantiates a new sparse instance data.
   *
   * @param attributeValues  the attribute values
   * @param indexValues      the index values
   * @param numberAttributes the number attributes
   */
  public FilteredSparseInstanceData(double[] attributeValues, int[] indexValues, int numberAttributes) {
    super(attributeValues, indexValues, numberAttributes);
  }


  /**
   * Value of the attribute in the indexAttribute position.
   * If this value is absent, a NaN value (marker of missing value)
   * is returned, otherwise this method returns the actual value.
   *
   * @param indexAttribute the index attribute
   * @return the double
   */
  @Override
  public double value(int indexAttribute) {
    int location = locateIndex(indexAttribute);
    if ((location >= 0) && (indexValues[location] == indexAttribute)) {
      return attributeValues[location];
    } else {
      // returns a NaN value which represents missing values instead of a 0 (zero)
      return Double.NaN;
    }
  }
}