Generate normal distribution / lognormal distribution random numbers in Java

Introduction

If you want to generate random numbers in Java, the first thing you can think of is Math.random (). However, the values ​​obtained by this are uniformly distributed, and all the values ​​appear with the same probability, so it is not suitable when you want to create the following dummy values.

--Test score ... The average score is most likely to appear, and the farther away from the average score, the less likely it is to appear. → ** Normal distribution ** --Annual household income ... Distribution that extends long to the right from the center of the graph → ** Lognormal distribution **

You can do your best to write the calculation formula (I did my best to write it), but since there was a library, let's use it.

normal distribution

Use nextGaussian in java.util.Random.

Random.html

import org.junit.jupiter.api.Test;

import java.util.List;
import java.util.Random;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class GaussianTest {

    @Test
    public void nextGaussianTest() {
        Random random = new Random();

        List<Double> results = IntStream.rangeClosed(1, 100000).boxed()
                .map(i -> random.nextGaussian() * 20 + 50) //Standard deviation 20, mean 50
                .collect(Collectors.toList());

        printResults(results);
    }

    private void printResults(List<Double> results) {
        for (int i = 0; i < 20; i++) {
            int start = i * 5;
            int end = (i + 1) * 5;
            double ratio = results.stream().filter(val -> (val >= start && val < end)).count() / 100000d * 100;
            System.out.println(start + "〜" + end + ": " + IntStream.rangeClosed(1, (int) ratio).mapToObj(val -> "■").collect(Collectors.joining("")));
        }
    }
}

The distribution looks like this.

0〜5: 
5〜10:  ■
10〜15: ■
15〜20: ■■
20〜25: ■■■
25〜30: ■■■■■
30〜35: ■■■■■■
35〜40: ■■■■■■■■
40〜45: ■■■■■■■■■
45〜50: ■■■■■■■■■
50〜55: ■■■■■■■■■
55〜60: ■■■■■■■■■
60〜65: ■■■■■■■■
65〜70: ■■■■■■
70〜75: ■■■■■
75〜80: ■■■
80〜85: ■■
85〜90: ■
90〜95: ■
95〜100: 	
# (* The number of spaces is adjusted to align the axes.)

Lognormal distribution

Use the Apache Commons LogNormalDistribution.

LogNormalDistribution.html

import org.apache.commons.math3.distribution.LogNormalDistribution;
import org.junit.jupiter.api.Test;

import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class GaussianTest {

    @Test
    public void logNormalDistributionTest() {
        double MU = 3.0; // ln(x)The larger the average μ of, the longer the right side of the graph
        double SIGMA = 1.0; // ln(x)Standard deviation of σ The larger the graph, the wider the graph.
        LogNormalDistribution distribution = new LogNormalDistribution(MU, SIGMA);

        List<Double> results = IntStream.rangeClosed(1, 100000).boxed()
                .map(i -> distribution.sample())
                .collect(Collectors.toList());

        printResults(results);
    }

    private void printResults(List<Double> results) {
        //Abbreviation
    }
}

The result is like this.

0〜5:   ■■■■■■■■
5〜10:  ■■■■■■■■■■■■■■■■
10〜15: ■■■■■■■■■■■■■■
15〜20: ■■■■■■■■■■■
20〜25: ■■■■■■■■
25〜30: ■■■■■■
30〜35: ■■■■■
35〜40: ■■■■
40〜45: ■■■
45〜50: ■■
50〜55: ■■
55〜60: ■■
60〜65: ■
65〜70: ■
70〜75: ■
75〜80: ■
80〜85: 
85〜90: 
90〜95: 
95〜100: 

reference

keisan.casio.jp Normal distribution (graph) keisan.casio.jp Lognormal distribution (graph)