在Rust中，如何从HashMap的键创建HashSet

发布于12月03日

我有两个HashMap，想要计算关键点的交点.有没有可能在HashMap::keys()个返回值中构造一个HashSet？例如:

use std::collections::{HashSet, HashMap};

fn main() {
    let mut map1: HashMap<i64, i64> = HashMap::new();
    let mut map2: HashMap<i64, i64> = HashMap::new();

    // Add some values into the HashMaps for demonstration
    map1.insert(1, 10);
    map1.insert(5, 50);
    map2.insert(3, 30);
    map2.insert(5, 50);

    let set1: HashSet<i64> = HashSet::from(map1.keys());  // How to do this?
    let set2: HashSet<i64> = HashSet::from(map2.keys());  // How to do this?

    let set3 = set1.intersection(&set2); // What I'm looking to accomplish
    // set3 should contain [5], as this is the one key shared by the two HashMaps
}

推荐答案

简单的解决方案

你的代码只需要一些调整就可以真正编译(see Playground):

use std::collections::{HashSet, HashMap};

fn main() {
    let mut map1 = HashMap::new();
    let mut map2 = HashMap::new();

    // Add some values into the HashMaps for demonstration
    map1.insert(1, 10);
    map1.insert(5, 50);
    map2.insert(3, 30);
    map2.insert(5, 50);

    let set1: HashSet<i64> = map1.keys().cloned().collect();
    let set2: HashSet<i64> = map2.keys().cloned().collect();

    let set3 = set1.intersection(&set2);
    println!("{:?}", set3);
}

特别是注map1.keys().cloned().collect():