C++. Weighted std::shuffle

问题

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);

回答1:

If OP intent is to shuffle a list r of items

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).

As stated in the page linked by Severin Pappadeux:

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.

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;
    }
}

Live example HERE.

来源：https://stackoverflow.com/questions/50221136/c-weighted-stdshuffle