/************************************************************************* * Compilation: javac StdStats.java * Execution: java StdStats < input.txt * * Library of statistical functions. * * The test client reads an array of real numbers from standard * input, and computes the minimum, mean, maximum, and * standard deviation. * * The functions all throw a NullPointerException if the array * passed in is null. * % more tiny.txt * 5 * 3.0 1.0 2.0 5.0 4.0 * * % java StdStats < tiny.txt * min 1.000 * mean 3.000 * max 5.000 * std dev 1.581 * *************************************************************************/ public final class StdStats { private StdStats() { } /** * Return maximum value in array, -infinity if no such value. */ public static double max(double[] a) { double max = Double.NEGATIVE_INFINITY; for (int i = 0; i < a.length; i++) { if (a[i] > max) max = a[i]; } return max; } /** * Return maximum value in subarray a[lo..hi], -infinity if no such value. */ public static double max(double[] a, int lo, int hi) { if (lo < 0 || hi >= a.length || lo > hi) throw new RuntimeException("Subarray indices out of bounds"); double max = Double.NEGATIVE_INFINITY; for (int i = lo; i <= hi; i++) { if (a[i] > max) max = a[i]; } return max; } /** * Return maximum value of array, Integer.MIN_VALUE if no such value */ public static int max(int[] a) { int max = Integer.MIN_VALUE; for (int i = 0; i < a.length; i++) { if (a[i] > max) max = a[i]; } return max; } /** * Return minimum value in array, +infinity if no such value. */ public static double min(double[] a) { double min = Double.POSITIVE_INFINITY; for (int i = 0; i < a.length; i++) { if (a[i] < min) min = a[i]; } return min; } /** * Return minimum value in subarray a[lo..hi], +infinity if no such value. */ public static double min(double[] a, int lo, int hi) { if (lo < 0 || hi >= a.length || lo > hi) throw new RuntimeException("Subarray indices out of bounds"); double min = Double.POSITIVE_INFINITY; for (int i = lo; i <= hi; i++) { if (a[i] < min) min = a[i]; } return min; } /** * Return minimum value of array, Integer.MAX_VALUE if no such value */ public static int min(int[] a) { int min = Integer.MAX_VALUE; for (int i = 0; i < a.length; i++) { if (a[i] < min) min = a[i]; } return min; } /** * Return average value in array, NaN if no such value. */ public static double mean(double[] a) { if (a.length == 0) return Double.NaN; double sum = sum(a); return sum / a.length; } /** * Return average value in subarray a[lo..hi], NaN if no such value. */ public static double mean(double[] a, int lo, int hi) { int length = hi - lo + 1; if (lo < 0 || hi >= a.length || lo > hi) throw new RuntimeException("Subarray indices out of bounds"); if (length == 0) return Double.NaN; double sum = sum(a, lo, hi); return sum / length; } /** * Return average value in array, NaN if no such value. */ public static double mean(int[] a) { if (a.length == 0) return Double.NaN; double sum = 0.0; for (int i = 0; i < a.length; i++) { sum = sum + a[i]; } return sum / a.length; } /** * Return sample variance of array, NaN if no such value. */ public static double var(double[] a) { if (a.length == 0) return Double.NaN; double avg = mean(a); double sum = 0.0; for (int i = 0; i < a.length; i++) { sum += (a[i] - avg) * (a[i] - avg); } return sum / (a.length - 1); } /** * Return sample variance of subarray a[lo..hi], NaN if no such value. */ public static double var(double[] a, int lo, int hi) { int length = hi - lo + 1; if (lo < 0 || hi >= a.length || lo > hi) throw new RuntimeException("Subarray indices out of bounds"); if (length == 0) return Double.NaN; double avg = mean(a, lo, hi); double sum = 0.0; for (int i = lo; i <= hi; i++) { sum += (a[i] - avg) * (a[i] - avg); } return sum / (length - 1); } /** * Return sample variance of array, NaN if no such value. */ public static double var(int[] a) { if (a.length == 0) return Double.NaN; double avg = mean(a); double sum = 0.0; for (int i = 0; i < a.length; i++) { sum += (a[i] - avg) * (a[i] - avg); } return sum / (a.length - 1); } /** * Return population variance of array, NaN if no such value. */ public static double varp(double[] a) { if (a.length == 0) return Double.NaN; double avg = mean(a); double sum = 0.0; for (int i = 0; i < a.length; i++) { sum += (a[i] - avg) * (a[i] - avg); } return sum / a.length; } /** * Return population variance of subarray a[lo..hi], NaN if no such value. */ public static double varp(double[] a, int lo, int hi) { int length = hi - lo + 1; if (lo < 0 || hi >= a.length || lo > hi) throw new RuntimeException("Subarray indices out of bounds"); if (length == 0) return Double.NaN; double avg = mean(a, lo, hi); double sum = 0.0; for (int i = lo; i <= hi; i++) { sum += (a[i] - avg) * (a[i] - avg); } return sum / length; } /** * Return sample standard deviation of array, NaN if no such value. */ public static double stddev(double[] a) { return Math.sqrt(var(a)); } /** * Return sample standard deviation of subarray a[lo..hi], NaN if no such value. */ public static double stddev(double[] a, int lo, int hi) { return Math.sqrt(var(a, lo, hi)); } /** * Return sample standard deviation of array, NaN if no such value. */ public static double stddev(int[] a) { return Math.sqrt(var(a)); } /** * Return population standard deviation of array, NaN if no such value. */ public static double stddevp(double[] a) { return Math.sqrt(varp(a)); } /** * Return population standard deviation of subarray a[lo..hi], NaN if no such value. */ public static double stddevp(double[] a, int lo, int hi) { return Math.sqrt(varp(a, lo, hi)); } /** * Return sum of all values in array. */ public static double sum(double[] a) { double sum = 0.0; for (int i = 0; i < a.length; i++) { sum += a[i]; } return sum; } /** * Return sum of all values in subarray a[lo..hi]. */ public static double sum(double[] a, int lo, int hi) { if (lo < 0 || hi >= a.length || lo > hi) throw new RuntimeException("Subarray indices out of bounds"); double sum = 0.0; for (int i = lo; i <= hi; i++) { sum += a[i]; } return sum; } /** * Return sum of all values in array. */ public static int sum(int[] a) { int sum = 0; for (int i = 0; i < a.length; i++) { sum += a[i]; } return sum; } /** * Plot points (i, a[i]) to standard draw. */ public static void plotPoints(double[] a) { int N = a.length; StdDraw.setXscale(0, N-1); StdDraw.setPenRadius(1.0 / (3.0 * N)); for (int i = 0; i < N; i++) { StdDraw.point(i, a[i]); } } /** * Plot line segments connecting points (i, a[i]) to standard draw. */ public static void plotLines(double[] a) { int N = a.length; StdDraw.setXscale(0, N-1); StdDraw.setPenRadius(); for (int i = 1; i < N; i++) { StdDraw.line(i-1, a[i-1], i, a[i]); } } /** * Plot bars from (0, a[i]) to (i, a[i]) to standard draw. */ public static void plotBars(double[] a) { int N = a.length; StdDraw.setXscale(0, N-1); for (int i = 0; i < N; i++) { StdDraw.filledRectangle(i, a[i]/2, .25, a[i]/2); } } /** * Test client. * Convert command-line arguments to array of doubles and call various methods. */ public static void main(String[] args) { double[] a = StdArrayIO.readDouble1D(); StdOut.printf(" min %7.3f\n", min(a)); StdOut.printf(" mean %7.3f\n", mean(a)); StdOut.printf(" max %7.3f\n", max(a)); StdOut.printf(" std dev %7.3f\n", stddev(a)); } }
Thursday, 12 July 2012
data analysis library
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data analysis library
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