How to sort a vector by indices in Rust-CodePudding

I want to sort a vector (inplace) by a predefined ordering in Rust.

For example

let i = vec![0, 3, 2, 1];
let mut v = vec!["a", "b", "c", "d"];
v.sort_by_index(&i);

assert_eq!(v, &["a", "d", "c", "b"]);

I would like to do this inplace. In my use case, v takes up a lot of memory.

Note: this question is a natural follow-on from How to get the indices that would sort a vector in Rust?

CodePudding user response：

In the same way it enough to implement yourself

let i = vec![0, 3, 2, 1];
let mut v = vec!["a", "b", "c", "d"];

v = i.into_iter().map(|x| v[x]).collect::<Vec<&str>>();

assert_eq!(v, &["a", "d", "c", "b"]);

CodePudding user response：

You can create a HashMap or BTreeMap lookup table and use it as key searcher:

use std::collections::HashMap;
fn main() {
    let i = vec![0, 3, 2, 1];
    let mut v = vec!["a", "b", "c", "d"];

    let keys: HashMap<_, _> = v.iter().cloned().zip(i.iter()).collect();
    v.sort_by_cached_key(|e| keys[e]);

    assert_eq!(v, &["a", "d", "c", "b"]);
}

Playground