Crate counter

Counter counts recurrent elements of iterables. It is based on the Python implementation.

The struct Counter is the entry-point type for this module.

Examples

Just count an iterable

use counter::Counter;
let char_counts = "barefoot".chars().collect::<Counter<_>>();
let counts_counts = char_counts.values().collect::<Counter<_>>();

Update a count

let mut counts = "aaa".chars().collect::<Counter<_>>();
counts[&'a'] += 1;
counts[&'b'] += 1;

let mut counts = "able babble table babble rabble table able fable scrabble"
    .split_whitespace().collect::<Counter<_>>();
// 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 = "scrabble cabbie fable babble"
    .split_whitespace().collect::<Counter<_>>();
let difference = counts - other_counts;

Extend a Counter with another Counter:

let mut counter = "abbccc".chars().collect::<Counter<_>>();
let another = "bccddd".chars().collect::<Counter<_>>();
counter.extend(&another);
let expect = [('a', 1), ('b', 3), ('c', 5), ('d', 3)].iter()
    .cloned().collect::<HashMap<_, _>>();
assert_eq!(counter.into_map(), expect);

Get items with keys

let counts = "aaa".chars().collect::<Counter<_>>();
assert_eq!(counts[&'a'], 3);
assert_eq!(counts[&'b'], 0);

Get the most common items

most_common_ordered() uses the natural ordering of keys which are Ord.

let by_common = "eaddbbccc".chars().collect::<Counter<_>>().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.

let counter = "eaddbbccc".chars().collect::<Counter<_>>();
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, N> implements Deref<Target=HashMap<T, N>> and DerefMut<Target=HashMap<T, N>>, which means that you can perform any operations on it which are valid for a HashMap.

let mut counter = "aa-bb-cc".chars().collect::<Counter<_>>();
counter.remove(&'-');
assert!(counter == "aabbcc".chars().collect::<Counter<_>>());

Note that Counter<T, N> itself implements Index. Counter::index returns a reference to a zero value for missing keys.

let counter = "aaa".chars().collect::<Counter<_>>();
assert_eq!(counter[&'b'], 0);
// panics
// assert_eq!((*counter)[&'b'], 0);

Advanced Usage

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.

#[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 = intys.iter().collect::<Counter<_>>();
println!("{:?}", inty_counts);
// {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.get(&Inty { i: 8 }) == Some(&2));
assert!(inty_counts.get(&Inty { i: 0 }) == Some(&3));
assert!(inty_counts.get(&Inty { i: 6 }) == Some(&1));

Use your own type for the count

Sometimes usize just isn't enough. If you find yourself overflowing your machine's native size, you can use your own type. Here, we use an i8, but you can use most numeric types, including bignums, as necessary.

let counter: Counter<_, i8> = "abbccc".chars().collect();
let expected: HashMap<char, i8> = [('a', 1), ('b', 2), ('c', 3)].iter().cloned().collect();
assert!(counter.into_map() == expected);

Structs

Counter