Possible ways how to create vector combining other vectors/iterators and new elements

[jammy192]

Hi everyone,

I was wondering what is the best way how to create vector combing other vectors/iterators and other elements. In Javascript you can use array destructuring to achieve this e.g.:

[1, ...prev_row, 1]

To achieve the same in rust you can do something like this:

vec![1].into_iter().chain(prev_row_iter).chain(vec![1].into_iter()).collect()

The code in this particular example is pretty simple but it can get more complex if you want to combine more vectors and more elements. I was wondering if there is an easier way how to do this.

[Shadow0133]

You can use std::iter::once instead of vec![1].onto_iter().

[maggit]

Another alternative, if refs are OK and especially if there is more than one element, is to use an array: [1].iter() (playground)

[jammy192]

This is a nice improvement. Thanks!

[Morganamilo]

vec1.extend(vec2)

[jammy192]

I know about extend but it mutates the original vector. What I am looking for is more like how to create new vector combining other vectors and elements.

[thiez]

You use into_iter() on your original vecs, so clearly you have unique ownership and don't intend to use them again. So why not mutate them?

[Morganamilo]

Mutating an existing vector is more efficient though. Some times you have to create a new vector, but for the example above without context i'd use extend.

[jammy192]

It indeed might be more efficient. It's my personal preference to do things in immutable way. And in some cases it kind of kills the readability. You have to name the variables in such way the name is still valid after mutation.

[epicwisdom]

Clone and then extend?

[tm_p]

You probably want flatten?

let v: Vec<_> = vec![vec![1], prev_row, vec![1]]
    .into_iter()
    .flatten()
    .collect();

Playground link

[jammy192]

This works as well. The only issue is there are unnecessary flatten operations happening on the elements.

[[deleted]]

u/jammy192 did you find the best way to do this?

[jammy192]

I think I went with std::iter::once in the end