How to iterate through a HashMap in parallel in Rust?

Question

I have a HashMap and want to iterate through its values in parallel using rayon. I cannot consume it and it is not feasible to first create a Vec from the values.

Does anyone have an idea on how to do this?

Answer 1

Does anyone have an idea on how to do this?

Rayon implements IntoParallelIterator for &HashMap.

So you can just call par_iter on the hashmap with rayon's prelude imported and it'll work: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=e710e23bcc99bd09ce4fab5ba7544604

use std::collections::HashMap;
use rayon::prelude::*;

fn main() {
    let h = HashMap::from([
        ("foo", 1),
        ("bar", 2),
        ("baz", 3),
        ("qux", 4),
        ("quux", 5),
    ]);
    thing(&h);
}

fn thing(m: &HashMap<&str, usize>) {
    let v: usize = m.par_iter()
        .map(|(_, v)| *v)
        .sum();
    println!("{}", v);
}