使用概率选择数组值 [英] Picking Array Values using Probability

问题描述

给定以下概率，从黄色，蓝色和红色中选择一种随机的颜色：黄色，蓝色和红色：3/7
蓝色：1/7
红色：3/7

Pick a random color, from yellow, blue and red, given the probability of: Yellow: 3/7 Blue: 1/7 Red: 3/7

我知道我可以使用以下方法解决此问题：
[黄色，黄色，黄色，蓝色，红色，红色，红色]
但是我认为这在编程上不会很好，因为当我偶然时的可能性，我将不得不更改数组。

I know that I could work this around by using something like: [yellow, yellow, yellow, blue, red, red, red] But I don't think this would be programatically good, since when I chance the probability, I would have to change the array.

所以，我想我可以尝试类似权重法

So, I thought I could try something like a weight approach

let yellow_probability = 3/7
let blue_probability = 1/7
let red_probability = 3/7

const colors = ['yellow', 'blue', 'red']

function pickPosition(yellow_probability, blue_probability, red_probability){

    let yellow_weight = Math.random() * yellow_probability
    let blue_weight = Math.random() * blue_probability
    let red_weight = Math.random() * red_probability

    let weights = [yellow_weight, blue_weight, red_weight]

    let max_of_array = Math.max.apply(Math, weights);

    pickedColor = weights.indexOf(max_of_array)

    return pickedColor

}
pickedColorIndex = pickPosition(yellow_probability, blue_probability, red_probability)
pickedColor = colors[pickedColorIndex]
console.log(pickedColor)

---

我做了一个测试：

---

I did a test:

let n=1000000; 
let yellow=0, blue=0, red=0; 
for (let i=0; i<n; i++) {

    pickedColorIndex = pickPosition(yellow_probability, blue_probability, red_probability)
    if (pickedColorIndex==0) yellow++
    else if (pickedColorIndex==1) blue++
    else red++;
}
console.log("yellow = " + yellow/n );
console.log("blue = " + blue/n );
console.log("red = " + red/n );

我希望此测试输出类似：

And I would expect this test to output something like:

Yellow = 0.43
Blue = 0.14
Red = 0.43

但是我得到：

Yellow = 0.48
Blue = 0.03
Red = 0.48

有趣的是，指出代码在概率相等时有效（1/3，1/3，1/3）或类似（1/2，1/2，0）

It is interesting to point out that the code works when the probabilities are equal (1/3, 1/3, 1/3) or something like (1/2, 1/2, 0)

任何人都可以指出我在做什么

Can anyone point out what I am doing wrong?

推荐答案

您创建了尽可能多的不同项目，而不是单个随机值，然后将其与最高价值。

Instead of a single random value, you create as many as different items you have and later take the one with the max value.

这会促进具有更高因数/概率的价值/项目。

This promotes values/items with a higher factor/probability.

您可以将一个随机值带入一个数组，然后检查随机值位于哪个间隔。接受此项。

Instead of this approach, you could take a single random value and take all probabilities into an array and check in which interval the random value is. Take this item.

编辑：代码

function getRandomIndex(probabilities) {
    var random = Math.random(),
        i;
        
    for (i = 0; i < probabilities.length; i++) {
        if (random < probabilities[i]) return i;
        random -= probabilities[i];
    }
    return probabilites.length - 1;
}

var probabilities = [3 / 7, 1 / 7, 3 / 7],
    j = 1e6,
    count = [0, 0, 0];

while (j--) count[getRandomIndex(probabilities)]++;

console.log(count);

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