[Easy] More Rustic syntax for retaining values and indices of Vec

help
1

Just wondering if there is a more functional / rustic approach to retaining both indices and values from a vector whose value satisfy a condition.

Working snippet as follows:


fn main() {
    let x = vec![1, 2, 3, 4];
    let mut indices = vec![];
    let mut keepers = vec![];
    for (i, v) in x.iter().enumerate() {
        if v % 2 == 0 {
            keepers.push(v);
            indices.push(i);
        }
    }
    // println!("{:?}-{:?}", indices, keepers);
}

Of course I can easily get the values by making x mutable and using x.retain, but would also like to know which indices have either been kept or lost in the process.

(Playground)

2

You can use .filter() on the enumerated iterator. Then you can process the filtered iterator as you want (for example collecting it into one or two vectors [collect or unzip], or processing it further).

2 Likes
3

Why not use a HashMap?

use std::collections::HashMap;
fn main() {
    let x = vec![1, 2, 3, 4];
    let mut my_hashmap = HashMap::new();
    for (i, v) in x.iter().enumerate() {
        if v % 2 == 0 {
            my_hashmap.insert(i.to_string(), v);
        }
    }
    for (k, v) in my_hashmap {
        println!("{}: {}", k,v);
    }
}
4

How about using Iterator::partition after enumerate?

5

maybe this:

    let k: HashMap<usize, u32> = x
        .iter()
        .copied()
        .enumerate()
        .filter(|(_, value)| value % 2u32 == 0)
        .collect();
6

Yes! Something like this for example

let x = vec![1, 2, 3, 4];
let (indices, keepers): (Vec<_>, Vec<_>) = x
    .iter()
    .copied()
    .enumerate()
    .filter(|(i, v)| *v % 2 == 0)
    .unzip();
7

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