multi_containers

This crate implements containers that can have duplicate values. If you have ever written a HashMap<K, HashSet<V>>, this crate is for you.

This crate is unstable and its API is subject to change at any time until 1.0.0.

This crate is comparable in spirit to these containers in other languages:

• Java's Guava library's Multimap and Multiset (which heavily inspired this crate).
• Python's collections.defaultdict(set) and collections.Counter.
• C++'s std::(unordered_)mutlimap and std::(unordered_)multiset.

Usage

The primary containers are MultiMap and MultiSet. See examples.rs for more examples.

MultiMap

MultiMap is a wrapper around Map<K, Set<V>>. You can either use the provided HashMultiMap or BTreeMultiMap, or provide your own types with MultiMapBuilder. The API is similar to what you would expect from HashMap<K, HashSet<V>>, with some additional methods related to the multiple values. For bookkeeping reasons, the inner sets are not exposed mutably. MultiMap also provides ways of iterating over (&K, &Set<V>), or over (&K, &V).

use multi_containers::HashMultiMap;
let mut map = HashMultiMap::new();
map.insert("a".to_string(), 1);
map.insert("a".to_string(), 2);
map.insert("b".to_string(), 3);
assert_eq!(map.get("a").unwrap().len(), 2);
assert_eq!(map.get("b").unwrap().len(), 1);

MultiSet

MultiSet is a wrapper around Map<V, usize>. It offers the semantics of a set, but allows for duplicate values. It offers iterators over unique (&V, usize), and non-unique &V.

use multi_containers::HashMultiSet;
let mut set = HashMultiSet::new();
set.insert(1);
set.insert(1);
set.insert_some(2, 3);
assert_eq!(set.count(&1), 2);
assert_eq!(set.count(&2), 3);

License: MIT