# Counter
Simple counter library for Rust iterables. Inspired by, and largely mimicing the API of, Python's [Counter](https://docs.python.org/3.5/library/collections.html#collections.Counter).
## Examples
### Just count an iterable
```rust
let char_counts = Counter::init("barefoot".chars());
let counts_counts = Counter::init(char_counts.values());
```
### Updates are simple
```rust
let mut counts = Counter::init("able babble table babble rabble table able fable scrabble".split_whitespace());
// add or subtract an iterable of the same type
counts += "cain and abel fable table cable".split_whitespace();
// or add or subtract from another Counter of the same type
let other_counts = Counter::init("scrabble cabbie fable babble".split_whitespace());
let difference = counts - other_counts;
```
### Get the most common items
`most_common_ordered()` uses the natural ordering of keys which are `Ord`.
```rust
let by_common = Counter::init("eaddbbccc".chars())
.most_common_ordered();
let expected = vec![('c', 3), ('b', 2), ('d', 2), ('a', 1), ('e', 1)];
assert!(by_common == expected);
```
### Get the most common items using your own ordering
For example, here we break ties reverse alphabetically.
```rust
let counter = Counter::init("eaddbbccc".chars());
let by_common = counter.most_common_tiebreaker(|&a, &b| b.cmp(&a));
let expected = vec![('c', 3), ('d', 2), ('b', 2), ('e', 1), ('a', 1)];
assert!(by_common == expected);
```
### Treat it like a Map
`Counter<T>` implements `Deref<Target=HashMap<T, usize>>` and
`DerefMut<Target=HashMap<T, usize>>`, which means that you can perform any operations
on it which are valid for a [`HashMap`](https://doc.rust-lang.org/std/collections/struct.HashMap.html).
```rust
let mut counter = Counter::init("aa-bb-cc".chars());
counter.remove(&'-');
assert!(counter == Counter::init("aabbcc".chars()));
```
### Count any iterable which is `Hash + Eq`
You can't use the `most_common*` functions unless T is also `Clone`, but simple counting works fine on a minimal data type.
```rust
#[derive(Debug, Hash, PartialEq, Eq)]
struct Inty {
i: usize,
}
impl Inty {
pub fn new(i: usize) -> Inty {
Inty { i: i }
}
}
// <https://en.wikipedia.org/wiki/867-5309/Jenny>
let intys = vec![
Inty::new(8),
Inty::new(0),
Inty::new(0),
Inty::new(8),
Inty::new(6),
Inty::new(7),
Inty::new(5),
Inty::new(3),
Inty::new(0),
Inty::new(9),
];
let inty_counts = Counter::init(intys);
println!("{:?}", inty_counts.map);
// {Inty { i: 8 }: 2, Inty { i: 0 }: 3, Inty { i: 9 }: 1, Inty { i: 3 }: 1,
// Inty { i: 7 }: 1, Inty { i: 6 }: 1, Inty { i: 5 }: 1}
assert!(inty_counts.map.get(&Inty { i: 8 }) == Some(&2));
assert!(inty_counts.map.get(&Inty { i: 0 }) == Some(&3));
assert!(inty_counts.map.get(&Inty { i: 6 }) == Some(&1));
```