Create a vector of pairs from a single vector in C++
c++, std, std-pair, stdvector, stl
Solution
Use Range-v3:
#include <range/v3/range/conversion.hpp>
#include <range/v3/view/transform.hpp>
#include <range/v3/view/chunk.hpp>
using namespace ranges;
using namespace ranges::views;
int main() {
std::vector<int> origin {1, 2, 3, 4, 5, 6, 7, 8};
std::vector<std::pair<int, int>> goal {{1, 2}, {3, 4}, {5, 6}, {7, 8}};
auto constexpr makePairFromRangeOf2 = [](auto two){
return std::make_pair(two.front(), two.back());
};
auto result = origin | chunk(2)
| transform(makePairFromRangeOf2)
| to_vector;
}
Notice that if you only have to loop on `result`, then you only need it to be a range, so you can leave `| to_vector` out, because you'll still be able to do `result.begin()` and `result.end()`, which is what makes `result` a range.
If you don't need the inner containers to truly be `std::pair`s, but your just happy with calling, say, `result.front().front()` instead of `result.front().first`, then you can leave also the `transform`, and just be happy with `auto result = origin | chunk(2);`.
You don't mention why you only want a standard solution. However consider that `<ranges>` is standard in C++20. Unfortunately that feature is not as powerful as pre-C++20 Range-v3 library. But it will be at some point (C++23?), I think without any doubts.
Problem
I have a single even-sized vector that I want to transform into a vector of pairs where each pair contains always two elements. I know that I can do this using simple loops but I was wondering if there is a nice standard-library tool for this? It can be assumed that the original vector always contains an even amount of elements. Example: ``` vector<int> origin {1, 2, 3, 4, 5, 6, 7, 8}; vector<pair<int, int>> goal { {1, 2}, {3, 4}, {5, 6}, {7, 8} }; ```