Question

how can I efficiently modify the elements of these two lists using stl algorithms:

std::list<std::pair<double, string> > listPair(10);
std::list<double> listA(10);

And in such a way that the first pair-element gets the corresponding double value from listA?

Answer 1

Here I assume listPair is already filled, because there’s no way to get that string otherwise.

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You could loop through the collections directly.

auto a_cur = listA.begin(), a_end = listA.end();
auto pair_cur = listPair.begin();
for (; a_cur != a_end; ++ a_cur, ++ pair_cur) {
    pair_cur->first = *a_cur;
}

or use the “binary” version of std::transform, but this will involve copying the string:

std::transform(listA.begin(), listA.end(), listPair.begin(), listPair.begin(),
               [](double a, std::pair<double, string> b) {
                   return std::make_pair(a, b.second);
               });