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From mdigg...@apache.org
Subject cvs commit: jakarta-commons-sandbox/math/src/java/org/apache/commons/math/stat StatUtils.java
Date Tue, 17 Jun 2003 22:55:39 GMT
mdiggory    2003/06/17 15:55:39

  Added:       math/src/java/org/apache/commons/math/stat StatUtils.java
  Log:
  Initial Addition of StatUtils. Some methods need review, implementation and possibly debugging
  
  Revision  Changes    Path
  1.1                  jakarta-commons-sandbox/math/src/java/org/apache/commons/math/stat/StatUtils.java
  
  Index: StatUtils.java
  ===================================================================
  /* ====================================================================
   * The Apache Software License, Version 1.1
   *
   * Copyright (c) 2003 The Apache Software Foundation.  All rights
   * reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   *
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in
   *    the documentation and/or other materials provided with the
   *    distribution.
   *
   * 3. The end-user documentation included with the redistribution, if
   *    any, must include the following acknowlegement:
   *       "This product includes software developed by the
   *        Apache Software Foundation (http://www.apache.org/)."
   *    Alternately, this acknowlegement may appear in the software itself,
   *    if and wherever such third-party acknowlegements normally appear.
   *
   * 4. The names "The Jakarta Project", "Commons", and "Apache Software
   *    Foundation" must not be used to endorse or promote products derived
   *    from this software without prior written permission. For written
   *    permission, please contact apache@apache.org.
   *
   * 5. Products derived from this software may not be called "Apache"
   *    nor may "Apache" appear in their names without prior written
   *    permission of the Apache Software Foundation.
   *
   * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
   * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
   * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
   * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
   * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
   * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
   * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
   * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   * ====================================================================
   *
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Apache Software Foundation.  For more
   * information on the Apache Software Foundation, please see
   * <http://www.apache.org/>.
   */
  package org.apache.commons.math.stat;
  
  /**
   * StatUtils provides easy static implementations of common double[] based
   * statistical methods. These return a single result value or in some cases, as
   * identified in the javadoc for each method, Double.NaN.
   *
   * @author <a href="mailto:mdiggory@apache.org">Mark Diggory</a>
   */
  public class StatUtils {
  
  	/**
       * The sum of the values that have been added to Univariate.
       * @param values Is a double[] containing the values
       * @return the sum of the values or Double.NaN if the array is empty
  	 */
  	public static double sum(double[] values) {
  		double accum = 0.0;
  		for (int i = 0; i < values.length; i++) {
  			accum += values[i];
  		}
  		return accum;
  	}
  
  	/**
       * Returns the sum of the squares of the available values.
       * @param values Is a double[] containing the values
       * @return the sum of the squared values or Double.NaN if the array is empty
  	 */
  	public static double sumSq(double[] values) {
  		double accum = 0.0;
  		for (int i = 0; i < values.length; i++) {
  			accum += Math.pow(values[i], 2.0);
  		}
  		return accum;
  	}
  
  	/**
       * Returns the <a href=http://www.xycoon.com/arithmetic_mean.htm>
       * arithmetic mean </a> of the available values 
       * @param values Is a double[] containing the values
       * @return the mean of the values or Double.NaN if the array is empty
  	 */
  	public static double mean(double[] values) {
  		return sum(values) / values.length;
  	}
  
      /**
       *      
       * @param values Is a double[] containing the values
       * @return the result, Double.NaN if no values for an empty array 
       * or 0.0 for a single value set.  
       */
      public static double standardDeviation(double[] values) {
          double stdDev = Double.NaN;
          if (values.length != 0) {
              stdDev = Math.sqrt(variance(values));
          }
          return (stdDev);
      }
      
  	/**
       * Returns the variance of the available values.
       * @param values Is a double[] containing the values
       * @return the result, Double.NaN if no values for an empty array 
       * or 0.0 for a single value set.  
  	 */
  	public static double variance(double[] values) {
  		double variance = Double.NaN;
          
  		if (values.length == 1) {
  			variance = 0;
  		} else if (values.length > 1) {
  			double mean = mean(values);
  			double accum = 0.0;
  			for (int i = 0; i < values.length; i++) {
  				accum += Math.pow((values[i] - mean), 2.0);
  			}
  			variance = accum / (values.length - 1);
  		}
  		return variance;
  	}
  
      /**
       * Returns the skewness of a collection of values.  Skewness is a 
       * measure of the assymetry of a given distribution. 
       * @param values Is a double[] containing the values
       * @return the skewness of the values or Double.NaN if the array is empty
       */
      public double skewness(double[] values) {
          // Initialize the skewness
          double skewness = Double.NaN;
  
          // Get the mean and the standard deviation
          double mean = mean(values);
          double stdDev = standardDeviation(values);
  
          // Sum the cubes of the distance from the mean divided by the 
          // standard deviation
          double accum = 0.0;
          for (int i = 0; i < values.length; i++) {
              accum += Math.pow((values[i] - mean) / stdDev, 3.0);
          }
  
          // Get N
          double n = values.length;
  
          // Calculate skewness
          skewness = (n / ((n - 1) * (n - 2))) * accum;
  
          return skewness;
      }
  
      /**
       * Returns the kurtosis for this collection of values. Kurtosis is a 
       * measure of the "peakedness" of a distribution.
       * @param values Is a double[] containing the values
       * @return the kurtosis of the values or Double.NaN if the array is empty
       */
      public double kurtosis(double[] values) {
          // Initialize the kurtosis
          double kurtosis = Double.NaN;
  
          // Get the mean and the standard deviation
          double mean = mean(values);
          double stdDev = standardDeviation(values);
  
          // Sum the ^4 of the distance from the mean divided by the 
          // standard deviation
          double accum = 0.0;
          for (int i = 0; i < values.length; i++) {
              accum += Math.pow((values[i] - mean) / stdDev, 4.0);
          }
  
          // Get N
          double n = values.length;
  
          double coefficientOne = (n * (n + 1)) / ((n - 1) * (n - 2) * (n - 3));
          double termTwo = ((3 * Math.pow(n - 1, 2.0)) 
                             / ((n - 2) * (n - 3))); 
          // Calculate kurtosis
          kurtosis = (coefficientOne * accum) - termTwo;
  
          return kurtosis;
      }
      
  	/**
       * Returns the maximum of the available values
       * @param values Is a double[] containing the values
  	 * @return the maximum of the values or Double.NaN if the array is empty
  	 */
  	public static double max(double[] values) {
  		double max = Double.NaN;
  		for (int i = 0; i < values.length; i++) {
  			if (i == 0) {
  				max = values[i];
  			} else {
  				max = Math.max(max, values[i]);
  			}
  		}
  		return max;
  	}
  
  	/**
       * Returns the minimum of the available values
       * @param values Is a double[] containing the values
  	 * @return the minimum of the values or Double.NaN if the array is empty
  	 */
  	public static double min(double[] values) {
  		double min = Double.NaN;
  		for (int i = 0; i < values.length; i++) {
  			if (i == 0) {
  				min = values[i];
  			} else {
  				min = Math.min(min, values[i]);
  			}
  		}
  		return min;
  	}
      
      /** 
       * Returns the mode of the values that have been added.  The mode is
       * the element which occurs with the most frequency
       * @return the mode
       */
      public static double mode(){
          // Mode depends on a refactor Freq class
          String msg = "mode() is not yet implemented";
          throw new UnsupportedOperationException(msg);
      }
      
      /** 
       * Returns the mode of the values that have been added.  The mode is
       * the element which occurs with the most frequency
       * @return the mode
       */
      public static double median(double[] values){
          // Mode depends on a refactor Freq class
          String msg = "median() is not yet implemented";
          throw new UnsupportedOperationException(msg);
      }
  }
  
  

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