javascript - 从数组中选择随机元素时如何获得平衡输出？

Question

作为一个有趣的项目，我正在开发一款板球模拟器游戏，其中一个主要方面是在每次投球时获得随机结果。

一般来说，在Test Cricket中，有以下几种可能:

"0", "1" happen very frequently (60% of the time)

"2", "3" happen moderately (25% of the the time)

"FOUR", "SIX", "OUT" happen rarely (10% of the time)

"WIDE BALL", "NO BALL" happen very rarely (2% of the time)

如果我有一个数组，例如:

var possible_outcomes = ["0","1","2","3","FOUR","SIX","OUT","WIDE BALL","NO BALL"];

当从 possible_outcomes 中抽取随机项目时，经过固定的迭代次数(比如 60)，获得上述概率的最佳方法是什么。

PS:如果你们中的一些人不了解这项运动，我很抱歉。我使用了几个与板球相关的术语，因为我不知道如何更好地解释。

Answer 1

我建议使用连续检查概率和随机数的其余部分。

此函数首先将返回值设置为最后一个可能的索引并迭代，直到其余随机值小于实际概率。

概率之和必须为一。

function getRandomIndexByProbability(probabilities) {
    var r = Math.random(),
        index = probabilities.length - 1;

    probabilities.some(function (probability, i) {
        if (r < probability) {
            index = i;
            return true;
        }
        r -= probability;
    });
    return index;
}

var i,
    action = ["0", "1", "2", "3", "FOUR", "SIX", "OUT", "WIDE BALL", "NO BALL", "other"],
    probabilities = [0.3, 0.3, 1 / 8, 1 / 8, 1 / 30, 1 / 30, 1 / 30, 0.01, 0.01, 0.03],
    count = {},
    index;

action.forEach(function (a) { count[a] = 0; });

for (i = 0; i < 1e6; i++) {
    index = getRandomIndexByProbability(probabilities);
    count[action[index]]++;
}

console.log(count);

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