How to transpose a vector of vectors in Rust?

Question

So I have a Vec<Vec<T>> where the first vector groups by hours of day and the inner vector by days of week. I would like to transpose somehow the vectors to have it first by days then by hours. Is there a simple way to do it in Rust?

EDIT: I mean, I know how to do it with 2 for loops but is there a smarter/shorter way to do it functionally

Answer 1

You can use some iterators:

fn transpose<T>(v: Vec<Vec<T>>) -> Vec<Vec<T>>
where
    T: Clone,
{
    assert!(!v.is_empty());
    (0..v[0].len())
        .map(|i| v.iter().map(|inner| inner[i].clone()).collect::<Vec<T>>())
        .collect()
}

As user4815162342 comments, here is a version without Clone:

fn transpose2<T>(v: Vec<Vec<T>>) -> Vec<Vec<T>> {
    assert!(!v.is_empty());
    let len = v[0].len();
    let mut iters: Vec<_> = v.into_iter().map(|n| n.into_iter()).collect();
    (0..len)
        .map(|_| {
            iters
                .iter_mut()
                .map(|n| n.next().unwrap())
                .collect::<Vec<T>>()
        })
        .collect()
}

Playground