modules/ml/src/main/java/org/apache/ignite/ml/math/distances/WeightedMinkowskiDistance.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.ignite.ml.math.distances;

import java.util.Arrays;
import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonProperty;
import org.apache.ignite.ml.math.exceptions.math.CardinalityException;
import org.apache.ignite.ml.math.primitives.vector.Vector;
import org.apache.ignite.ml.math.primitives.vector.VectorUtils;
import org.apache.ignite.ml.math.util.MatrixUtil;

/**
 * Calculates the Weighted Minkowski distance between two points.
 */
public class WeightedMinkowskiDistance implements DistanceMeasure {
  /**
   * Serializable version identifier.
   */
  private static final long serialVersionUID = 1771556549784040096L;

  /** */
  private int p = 1;

  /** */
  private final double[] weights;

  /** */
  @JsonIgnore
  private final Vector internalWeights;

  /** */
  @JsonCreator
  public WeightedMinkowskiDistance(@JsonProperty("p")int p, @JsonProperty("weights")double[] weights) {
    this.p = p;
    this.weights = weights.clone();
    internalWeights = VectorUtils.of(weights).copy().map(x -> Math.pow(Math.abs(x), p));
  }

  /**
   * {@inheritDoc}
   */
  @Override public double compute(Vector a, Vector b)
      throws CardinalityException {

    return Math.pow(
        MatrixUtil.localCopyOf(a).minus(b)
            .map(x -> Math.pow(Math.abs(x), p))
            .times(internalWeights)
            .sum(),
        1 / (double) p
    );
  }

  /** Returns p-norm. */
  public int getP() {
    return p;
  }

  /** Returns weights. */
  public double[] getWeights() { return weights.clone(); }

  /**
   * {@inheritDoc}
   */
  @Override public boolean equals(Object obj) {
    if (this == obj) {
      return true;
    }

    return obj != null && getClass() == obj.getClass();
  }

  /**
   * {@inheritDoc}
   */
  @Override public int hashCode() {
    return getClass().hashCode();
  }

  /** {@inheritDoc} */
  @Override public String toString() {
    return "WeightedMinkowskiDistance{" +
        "p=" + p +
        ", weights=" + Arrays.toString(weights) +
        '}';
  }
}