samoa-api/src/main/java/org/apache/samoa/moa/core/MiscUtils.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.moa.core;

import java.io.PrintWriter;
import java.io.StringWriter;
import java.util.Random;

/**
 * Class implementing some utility methods.
 * 
 * @author Richard Kirkby (rkirkby@cs.waikato.ac.nz)
 * @author Bernhard Pfahringer (bernhard@cs.waikato.ac.nz)
 * @version $Revision: 7 $
 */
public class MiscUtils {

  public static int chooseRandomIndexBasedOnWeights(double[] weights,
      Random random) {
    double probSum = Utils.sum(weights);
    double val = random.nextDouble() * probSum;
    int index = 0;
    double sum = 0.0;
    while ((sum <= val) && (index < weights.length)) {
      sum += weights[index++];
    }
    return index - 1;
  }

  public static int poisson(double lambda, Random r) {
    if (lambda < 100.0) {
      double product = 1.0;
      double sum = 1.0;
      double threshold = r.nextDouble() * Math.exp(lambda);
      int i = 1;
      int max = Math.max(100, 10 * (int) Math.ceil(lambda));
      while ((i < max) && (sum <= threshold)) {
        product *= (lambda / i);
        sum += product;
        i++;
      }
      return i - 1;
    }
    double x = lambda + Math.sqrt(lambda) * r.nextGaussian();
    if (x < 0.0) {
      return 0;
    }
    return (int) Math.floor(x);
  }

  public static String getStackTraceString(Exception ex) {
    StringWriter stackTraceWriter = new StringWriter();
    ex.printStackTrace(new PrintWriter(stackTraceWriter));
    return "*** STACK TRACE ***\n" + stackTraceWriter.toString();
  }

  /**
   * Returns index of maximum element in a given array of doubles. First maximum is returned.
   * 
   * @param doubles
   *          the array of doubles
   * @return the index of the maximum element
   */
  public static/* @pure@ */int maxIndex(double[] doubles) {

    double maximum = 0;
    int maxIndex = 0;

    for (int i = 0; i < doubles.length; i++) {
      if ((i == 0) || (doubles[i] > maximum)) {
        maxIndex = i;
        maximum = doubles[i];
      }
    }

    return maxIndex;
  }
}