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

package org.apache.samoa.moa.core;

/*
 * #%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%
 */

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;
  }
}