Function map_keys 

pub fn map_keys<K, V, R, F>(map: &HashMap<K, V>, iteratee: F) -> BTreeMap<R, V>
where
    K: Eq + Hash + Ord,
    V: Clone,
    R: Ord,
    F: Fn(&V, &K) -> R,

Transforms the keys of a map using a provided function.

Arguments

• map - The input map whose keys are to be transformed.
• iteratee - A function that takes a reference to a value and its key, returning a new key.

Returns

• BTreeMap<R, V> - A new map with transformed keys.

Examples

use lowdash::map_keys;
use std::collections::HashMap;

let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
let transformed = map_keys(&map, |&v, &k| format!("key_{}", k));
assert_eq!(transformed.get("key_a"), Some(&1));
assert_eq!(transformed.get("key_b"), Some(&2));