StandardDeviation.java

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner; //Scanner import

public class StandardDeviation {

	// Constants to check from where to read the file
	public static final int READ_DATA_FROM_FILE = 1;
	public static final int READ_DATA_FROM_KEYBOARD = 2;
	
	public static void main(String[] args)

	{
		// declare the variable for the dataset, but don't initialise it yet.
		double[] dataset = null;
		Scanner sc = new Scanner(System.in);

		// declare a String variable for the filename
		String fileName;

		// declare a boolean to decide from where to get the data


		// First, check if the user passed anything as commandline argument
		// args is the array for commandline parameters. If no argument
		// was passed, the length = 0, if no arguments were passed, display a
		// Menu to let
		// the use choose.
		if ((args.length == 0) || (args.length == 2)) { // no commandline parameters
			// or 2 parameters given
			int choice = processMenu(sc); // Returns 1 or 2 depending on user Choice
			if (choice == READ_DATA_FROM_FILE) {
				fileName = getFileName(sc); // getFileName returns a valid filename in any case
				// Get File and process file
				// declare a variable for a File
				File aFile = getValidFile(fileName);
				dataset = getDataFromFile(aFile);
			}
			else {
				// get the data from the keyboard
				dataset = getDataFromKeyboard(sc);
			}
		} 
		if (args.length == 1) { // 1 commandline parameter -> Filename
			fileName = args[0];
			// get File and process file
			if (!isValidFile(fileName)) { // if the filename entered is not valid
				// ask the user to enter a valid file.
				fileName = getFileName(sc);
			}
			// declare a variable for a File
			File aFile = getValidFile(fileName);
			dataset = getDataFromFile(aFile);
		}
		if (args.length > 2) { // if more than 2 parameters are given, the
			//args[] are assumed to be the data
			dataset = convertStringArrayToDoubleArray(args);
		}
		// All options are evaluated,
		// the dataset is filled with data
		// calculate and display the statistics
		sc.close();
		showStatistics(dataset);
	}

	static void showStatistics(double[] dataset) {

		// calculate the results
		double mean = getMeanValue(dataset);
		double max = getMaxValue(dataset);
		double min = getMinValue(dataset);
		double std = getStdDev(dataset);

		// Show results
		System.out.println("Standard Deviation Information:");
		System.out.println("ô¿ô- ô¿ô- ô¿ô- ô¿ô- ô¿ô- ô¿ô- ");
		System.out.println("The mean is:" + mean);
		System.out.println("The minimum is:" + min);
		System.out.println("The Maximum is:" + max);
		System.out.println("The Standard deviation:" + std);

	}

	// Method for Data Entry
	public static double[] getDataFromKeyboard(Scanner sc) {
		int numberOfDataPoints = 0;
		do {
			System.out.println("Statistical data is to be entered from keybord");
			System.out.println();
			System.out.println("Enter number of items (minimum 3 items):");
			numberOfDataPoints = sc.nextInt();
			if (numberOfDataPoints < 3) {
				System.out
						.println("The number of data points should be greater than 2.");

			}
		} while (numberOfDataPoints < 3);

		// declare an array of n size to store integral data points
		double[] dataset = new double[numberOfDataPoints];
		// allow user inputs
		for (int i = 0; i < numberOfDataPoints; i++) {
			System.out.print("[" + i + "]:");
			dataset[i] = sc.nextDouble();
		}
		return dataset;
	}

	// Method for reading data from file
	public static double[] getDataFromFile(File aFile) {
		ArrayList<Double> tmp = new ArrayList<Double>();
		double[] arrtmp = null;
		Scanner scan = null;
		try {
			scan = new Scanner(aFile).useDelimiter("\\s*\\n");

			while(scan.hasNextDouble())
			{
				tmp.add(scan.nextDouble());
			}
			arrtmp = new double[tmp.size()];
			for (int i = 0; i < tmp.size(); i++) {
				arrtmp[i] = (double)tmp.get(i);
			}
		} catch (FileNotFoundException e1) {
			e1.printStackTrace();
		}
		if (scan != null) {
			scan.close();
		}
		return arrtmp;
	}

	// Method to calculate the mean
	public static double getMeanValue(double[] data) {
		double sum = 0.0;
		for (double d : data) {
			sum += d;
		}
		return sum / data.length;
	}

	// Method to find the maximum
	public static double getMaxValue(double[] data) {
		double max = Double.MIN_VALUE;
		for (double d : data) {
			if (d > max) {
				max = d;
			}
		}
		return max;
	}

	// Method to find the minimum
	public static double getMinValue(double[] data) {
		double min = Double.MAX_VALUE;
		for (double d : data) {
			if (d < min) {
				min = d;
			}
		}
		return min;
	}

	// Method to find the standard Deviation
	public static double getStdDev(double[] data) {
		double temp = 0.0;
		double mean = getMeanValue(data);

		for (double d : data) {
			temp = temp + Math.pow(d - mean, 2);
		}

		double std = Math.sqrt(temp / (data.length - 1));
		return std;
	}

	public static boolean isValidFile(String fileName) {
		File theFile = new File(fileName);
		return theFile.isFile();

	}

	public static File getValidFile(String fileName) {
		File theFile = new File(fileName);
		return theFile;
	}

	public static int processMenu(Scanner sc) {
		int response = 0;
		do {
			System.out.println("Statistics evaluation");
			System.out.println("---------------------");
			System.out.println();
			System.out.println("Please select:");
			System.out.println("1..to enter a filename and read data from a file");
			System.out.println("2..to enter the data from the keyboard");
			System.out.println("------------------------------------------------");
			System.out.println();
			System.out.print("Please enter 1 or 2:");
			response = sc.nextInt();
		} while ((response < 1) && (response > 2));
		return response;
	}

	public static String getFileName(Scanner sc) {
		String aFileName;
		do {
			System.out.println("Please enter a valid filename: ");
			aFileName = sc.nextLine();
		} while (!isValidFile(aFileName));	
		return aFileName;
	}
	
	
	// Helper method to convert a
	// String array to a double array
	public static double[] convertStringArrayToDoubleArray(String[] data) {
		double[] doubleData = new double[data.length];
		for (int i = 0; i < data.length; i++) {
			doubleData[i] = Double.parseDouble(data[i]);
		}
		return doubleData;
	}

}