Java中的随机加权选择 [英] Random weighted selection in Java

问题描述

我想从一组中选择一个随机项目，但是选择任何项目的机会应该与相关权重成正比。

I want to choose a random item from a set, but the chance of choosing any item should be proportional to the associated weight

示例输入：

item                weight
----                ------
sword of misery         10
shield of happy          5
potion of dying          6
triple-edged sword       1

所以，如果我有4个可能的项目，获得任何一个没有权重的项目的机会将是1/4。

So, if I have 4 possible items, the chance of getting any one item without weights would be 1 in 4.

在这种情况下，用户应该是10倍获得与三刃剑相当的痛苦之剑。

In this case, a user should be 10 times more likely to get the sword of misery than the triple-edged sword.

如何在Java中进行加权随机选择？

How do I make a weighted random selection in Java?

推荐答案

我将使用NavigableMap

I would use a NavigableMap

public class RandomCollection<E> {
    private final NavigableMap<Double, E> map = new TreeMap<Double, E>();
    private final Random random;
    private double total = 0;

    public RandomCollection() {
        this(new Random());
    }

    public RandomCollection(Random random) {
        this.random = random;
    }

    public RandomCollection<E> add(double weight, E result) {
        if (weight <= 0) return this;
        total += weight;
        map.put(total, result);
        return this;
    }

    public E next() {
        double value = random.nextDouble() * total;
        return map.higherEntry(value).getValue();
    }
}

说我有一个动物狗，猫，马的概率分别为40％，35％，25％

Say I have a list of animals dog, cat, horse with probabilities as 40%, 35%, 25% respectively

RandomCollection<String> rc = new RandomCollection<>()
                              .add(40, "dog").add(35, "cat").add(25, "horse");

for (int i = 0; i < 10; i++) {
    System.out.println(rc.next());
} 

这篇关于Java中的随机加权选择的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！