C ++.加权std :: shuffle [英] C++. Weighted std::shuffle

问题描述

有没有一种方法可以使用标准库进行漂亮而优雅的加权改组? 有std::discrete_distribution. 我想要的是这样的:

Is there a way to do nice and elegant weighted shuffling using standard library? There is std::discrete_distribution. What I want is something like this:

std::vector<T> data { N elements };
std::vector<int> weights { N weights };
std::shuffle(std::begin(data), std::end(data), something based on discrete distribution);

推荐答案

如果OP意图是对项目列表 r 进行洗牌

If OP intent is to shuffle a list r of items

这样，在给定权重列表 w 的情况下，权重为 w [i] 的元素 a [i] 应该是第一个随机洗牌 r 的元素，概率为 w [i]/sum(w).

such that, given a list of weights w, the element a[i] with weight w[i] should be the first element of the random shuffle r with probability w[i]/sum(w).

由页面中所述://stackoverflow.com/users/4044696/severin-pappadeux">Severin Pappadeux :

As stated in the page linked by Severin Pappadeux:

加权随机混洗与列表a中的加权随机采样相同，没有替换.即，以概率w [i]/sum(w)从a中选择元素a [i].将此元素存储在列表r中.然后，从a中删除元素a [i]，从w中删除w [i]，并从修改后的列表a中选择一个新元素，依此类推，直到a为空.

Weighted random shuffling is the same as weighted random sampling from a list a without replacement. That is, choose with probability w[i]/sum(w) element a[i] from a. Store this element in a list r. Then, remove element a[i] from a and w[i] from w, and select a new element of the modified list a, and so on until a is empty.

我不知道标准库中的这种算法，但是一个简单的实现可以是:

I'am not aware of such an algorithm in the Standard Library, but a simple implementation could be:

#include <random>
#include <algorithm>
#include <iterator>

template <class D, class W, class URBG>
void weighted_shuffle
    ( D first, D last
    , W first_weight, W last_weight
    , URBG&& g )
{
    while (first != last and first_weight != last_weight)
    {
        std::discrete_distribution dd(first_weight, last_weight);
        auto i = dd(g);
        if ( i )
        {
            std::iter_swap(first, std::next(first, i));
            std::iter_swap(first_weight, std::next(first_weight, i));
        }
        ++first;
        ++first_weight;
    }
}

实时示例此处.

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