// Arup Guha
// 2/9/06
// A small example that utilizes an array of arrays.
import java.util.*;
import java.io.*;

public class ProcessData {

  	public static void main(String[] args) throws IOException {

    	// Create the 2D array reference.
    	int[][] rawdata;

    	Scanner fin = new Scanner(new File("testdata.in"));
 
    	// Read in the number of regions in the data file.
    	int numregions = fin.nextInt();

    	// Allocate space for each array reference, one per region.
    	rawdata = new int[numregions][];

    	// Read in data for each region, one by one.
    	for (int i=0; i<numregions; i++) {

      		// Read in the number of samples for this particular region.
      		int numsamples = fin.nextInt();

      		// Allocate the space for this one array, to hold data for this region.
      		rawdata[i] = new int[numsamples];

      		// Read in each sample for this region.
      		for (int j=0; j<numsamples; j++)
        		rawdata[i][j] = fin.nextInt();
    	}

    	// Print out the standard deviation for each region.
    	for (int i=0; i<numregions; i++) {
      		System.out.print("Standard Deviation of Data Set "+(i+1));
      		System.out.println(": "+ stddev(rawdata[i]));
    	}

    	fin.close();
  	}

  	// Returns the average of the values stored in data.
  	public static double avg(int[] data) {
    	int sum = 0;

    	// Add up the sum of the values in data.
    	for (int i=0; i<data.length; i++) 
      		sum += data[i];

    	// Return the average by dividing this by the length of the array.
    	return (double)sum/data.length;
  	}

  	// Calculates the standard deviation of all of the values in data.
  	public static double stddev(int[] data) {

    	// Calculate the average of all the values.
    	double average = avg(data);
    	double sum=0;

    	// Add up the difference each term and the average squared.
    	for (int i=0; i<data.length; i++)
      		sum = sum + Math.pow((data[i]-average),2);

    	// Divide by the number of terms.
    	sum /= data.length;

    	// The standard deviation is the square root of that value.
    	return Math.sqrt(sum);
  	}
}