Possible solution for SO question #13541243

vectors.cpp

#include <vector>
#include <numeric>
#include <functional>

template<typename T>
std::vector<T> compact(const std::vector<T> &input, int stride, std::function<T(T, T)> op) {
	std::vector<T> output(stride);
	unsigned int index = 0;
	return std::accumulate(input.begin(), input.end(), output, [&index, stride, op](std::vector<T> &acc, T elem) -> std::vector<T> {
		acc[index % stride] = op(acc[index % stride], elem);
		++index;
		return acc;
	});
}

int main(int argc, char* argv[])
{
	std::vector<int> input;
	for(unsigned int i = 1; i < 11; ++i) {
		input.push_back(i);
	}
	
	auto output = compact(input, 3, std::function<int(int, int)>([](int l, int r) {
		return l + r;
	}));

	return 0;
}