Statistics.java :  » Game » rugl » com » ryanm » util » math » Java Open Source

package com.ryanm.util.math;

import java.nio.ShortBuffer;

/**
 * @author ryanm
 */
public class Statistics
{
  /**
   * Calculates the mean and the standard deviation
   * 
   * @param values
   *           The input values. NaN values will be ignored
   * @return A two element array, the first element is the mean
   *         value, the second is the standard deviation. Or null if
   *         value is null or empty, or entirely NaN filled
   */
  public static double[] calculateMeanDeviation( double[] values )
  {
    if( values != null && values.length > 0 )
    {
      double mean = 0;
      int count = 0;

      for( int i = 0; i < values.length; i++ )
      {
        if( !Double.isNaN( values[ i ] ) )
        {
          mean += values[ i ];
          count++;
        }
      }

      if( count == 0 )
      {
        return null;
      }

      mean /= count;

      double variance = 0;

      for( int i = 0; i < values.length; i++ )
      {
        if( !Double.isNaN( values[ i ] ) )
        {
          double delta = values[ i ] - mean;
          variance += delta * delta;
        }
      }

      variance /= count;

      double deviation = Math.sqrt( variance );

      return new double[] { mean, deviation };
    }

    return null;
  }

  /**
   * Calculates the mean and the standard deviation
   * 
   * @param values
   *           The input values.
   * @return A two element array, the first element is the mean
   *         value, the second is the standard deviation. Or null if
   *         value is null or empty, or entirely NaN filled
   */
  public static double[] calculateMeanDeviation( ShortBuffer values )
  {
    if( values != null && values.limit() > 0 )
    {
      double mean = 0;
      int count = 0;

      for( int i = 0; i < values.limit(); i++ )
      {
        mean += values.get( i );
        count++;
      }

      if( count == 0 )
      {
        return null;
      }

      mean /= count;

      double variance = 0;

      for( int i = 0; i < values.limit(); i++ )
      {
        double delta = values.get( i ) - mean;
        variance += delta * delta;
      }

      variance /= count;

      double deviation = Math.sqrt( variance );

      return new double[] { mean, deviation };
    }

    return null;
  }
}