Calculate SD

Monday, 20 June 2011 02:25

this simple program will calculate the SD(standard deviation) for the given input.



public class StandardDeviation{

   public static double mean ( double[] data )



      {



      double mean = 0;

      final int n = data.length;

      if ( n < 2 )

         return Double.NaN;

      for ( int i=0; i         mean += data[i];

      mean /= n;

      double sum = 0;

      for ( int i=0; i         {

         final double v = data[i] - mean;

         sum += v * v;

         }

      return Math.sqrt( sum / ( n - 1 ) );

      }

   public static double sd  ( double[] data ){



      final int n = data.length;



      if ( n < 2 )

         return Double.NaN;

      double avg = data[0];

      double sum = 0;

      for ( int i = 1; i < data.length; i++ )

         {

         double newavg = avg + ( data[i] - avg ) / ( i + 1 );

         sum += ( data[i] - avg ) * ( data [i] -newavg ) ;

         avg = newavg;

         }

      return Math.sqrt( sum / ( n - 1 ) );

      }

   public static void main ( String[] args )

      {

      double[] data = { 10, 100 , 50};

      System.out.println(mean(data));

      System.out.println(sd (data));

      }

   }

Know more theory about standard deviation Standard Deviation Calculator