rust - Are there equivalents to slice::chunks/windows for iterators to loop over pairs, triplets etc?

Question

It can be useful to iterate over multiple variables at once, overlapping (slice::windows), or not (slice::chunks).

This only works for slices; is it possible to do this for iterators, using tuples for convenience?

Something like the following could be written:

for (prev, next) in some_iter.windows(2) {
    ...
}

If not, could it be implemented as a trait on existing iterators?

Answer 1

It's possible to take chunks of an iterator using Itertools::tuples, up to a 4-tuple:

use itertools::Itertools; // 0.9.0

fn main() {
    let some_iter = vec![1, 2, 3, 4, 5, 6].into_iter();

    for (prev, next) in some_iter.tuples() {
        println!("{}--{}", prev, next);
    }
}

(playground)

1--2
3--4
5--6

If you don't know that your iterator exactly fits into the chunks, you can use Tuples::into_buffer to access any leftovers:

use itertools::Itertools; // 0.9.0

fn main() {
    let some_iter = vec![1, 2, 3, 4, 5].into_iter();

    let mut t = some_iter.tuples();
    for (prev, next) in t.by_ref() {
        println!("{}--{}", prev, next);
    }
    for leftover in t.into_buffer() {
        println!("{}", leftover);
    }
}

(playground)

1--2
3--4
5

It's also possible to take up to 4-tuple windows with Itertools::tuple_windows:

use itertools::Itertools; // 0.9.0

fn main() {
    let some_iter = vec![1, 2, 3, 4, 5, 6].into_iter();

    for (prev, next) in some_iter.tuple_windows() {
        println!("{}--{}", prev, next);
    }
}

(playground)

1--2
2--3
3--4
4--5
5--6

If you need to get partial chunks / windows, you can get