CODEWITHSUNDEEP
rust
biofractal
biofractal

Reputation: 19143

How do I create a union of two vecs where the union contains references to the original vec members?

I want to process all the items in two unequally sized vecs as if they were a single unified vec.

The approach I have taken is to create a union of the two vecs using concat however this method clones the items so that when I process the union's items the changes are applied to the clones and not to the original items.

How can I create a union of references to the original items so that when I process the items in the union I am actually processing the items in the two vecs?

pub struct Model {
    pub population: Vec<Item>,
    pub archive: Vec<Item>,
}

pub struct Item {
    pub fitness: f32,
}

pub fn process_union(model: &Model) {
    let mut union = [&model.population[..], &model.archive[..]].concat(); 
    union.iter_mut().for_each(|item| {
        item.fitness += 1.0;
    });
}

#[test]
fn test_union() {
    let model = Model::default();
    process_union(&model);
    assert_eq!(model.population[0].fitness, 1.0);
    assert_eq!(model.archive[0].fitness, 1.0);
}

Upvotes: 1

Views: 1952

Answers (1)

Carson
Carson

Reputation: 3129

Two small changes can make your code work.

First, if you want a function to process data in place, you need to use an &mut pointer, as compared to a normal &. &mut gives you the ability to modify the data you are passed.

Second, iterator chaining is probably exactly what you need! Check out this modified form of your example:

pub struct Model {
    pub population: Vec<Item>,
    pub archive: Vec<Item>,
}

pub struct Item {
    pub fitness: f32,
}

pub fn process_union(model: &mut Model) {
    model.population.iter_mut()
        .chain(model.archive.iter_mut())
        .for_each(|item| {
            item.fitness += 1.0;
        });
}

#[test]
fn test_union() {
    let mut model = Model::default();
    process_union(&mut model);
    assert_eq!(model.population[0].fitness, 1.0);
    assert_eq!(model.archive[0].fitness, 1.0);
}

Upvotes: 1

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