53 lines
1.6 KiB
Java
53 lines
1.6 KiB
Java
import static java.lang.Math.pow;
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import static java.util.Arrays.stream;
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import static java.util.stream.Collectors.joining;
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import static java.util.stream.IntStream.range;
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public class Test {
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static double[] meanStdDev(double[] numbers) {
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if (numbers.length == 0)
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return new double[]{0.0, 0.0};
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double sx = 0.0, sxx = 0.0;
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long n = 0;
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for (double x : numbers) {
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sx += x;
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sxx += pow(x, 2);
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n++;
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}
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return new double[]{sx / n, pow((n * sxx - pow(sx, 2)), 0.5) / n};
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}
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static String replicate(int n, String s) {
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return range(0, n + 1).mapToObj(i -> s).collect(joining());
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}
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static void showHistogram01(double[] numbers) {
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final int maxWidth = 50;
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long[] bins = new long[10];
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for (double x : numbers)
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bins[(int) (x * bins.length)]++;
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double maxFreq = stream(bins).max().getAsLong();
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for (int i = 0; i < bins.length; i++)
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System.out.printf(" %3.1f: %s%n", i / (double) bins.length,
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replicate((int) (bins[i] / maxFreq * maxWidth), "*"));
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System.out.println();
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}
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public static void main(String[] a) {
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Locale.setDefault(Locale.US);
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for (int p = 1; p < 7; p++) {
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double[] n = range(0, (int) pow(10, p))
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.mapToDouble(i -> Math.random()).toArray();
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System.out.println((int)pow(10, p) + " numbers:");
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double[] res = meanStdDev(n);
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System.out.printf(" Mean: %8.6f, SD: %8.6f%n", res[0], res[1]);
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showHistogram01(n);
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}
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}
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}
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