package org.apache.samoa.instances;

/*
 * #%L
 * SAMOA
 * %%
 * Copyright (C) 2014 - 2015 Apache Software Foundation
 * %%
 * Licensed 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.
 * #L%
 */

/**
 * 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;
    }
  }
}