Transpose vector of vectors with views::zip

Question

Duplicate: https://stackoverflow.com/a/61819663/11998382

This should be possible if we know the size of the outer vector at compile time.

You just have to write the c++ variadic-template equivalent of the following python code:

def transpose(rng_of_rng):
    return zip(*rng_of_rng)

"*This should be possible if we know the size of the outer vector at compile time.*" How is this possible for `vector`? — 康桓瑋, Feb 09 '23 at 02:09
@康桓瑋 I mean you are using `std::vector` as a `std::unique_ptr` — Tom Huntington, Feb 09 '23 at 02:21

score 0 · Accepted Answer · answered Feb 09 '23 at 00:08

template <std::size_t N, typename T>
auto transpose(std::span<T, N> rng_rng)
{
    return [&] <std::size_t... I>(std::index_sequence<I...>)
    {
        return  ranges::views::zip( rng_rng[I]... );
    }(std::make_integer_sequence<std::size_t, N>{});
}

And here it is in action: https://godbolt.org/z/oPdn89qnT

I found barry's answer really useful when trying to convert a vector into a static-extent span.

On second thought, maybe this idea isn't so great because be get out a range of tuples. I'm only working with N=10, but I doubt it would be good to have really big tuple sizes.

Transpose vector of vectors with views::zip

1 Answers1