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);
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.
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