Struct counter::Counter

pub struct Counter<T: Hash + Eq, N = usize> { /* fields omitted */ }

Implementations

impl<T, N> Counter<T, N> where
    T: Hash + Eq,
    N: PartialOrd + AddAssign + SubAssign + Zero + One, 

pub fn new() -> Counter<T, N>

Create a new, empty Counter

pub fn init<I>(iterable: I) -> Counter<T, N> where
    I: IntoIterator<Item = T>, 

Create a new Counter initialized with the given iterable

pub fn update<I>(&mut self, iterable: I) where
    I: IntoIterator<Item = T>, 

Add the counts of the elements from the given iterable to this counter

pub fn into_map(self) -> HashMap<T, N>

Consumes this counter and returns a HashMap mapping the items to the counts.

pub fn subtract<I>(&mut self, iterable: I) where
    I: IntoIterator<Item = T>, 

Remove the counts of the elements from the given iterable to this counter

Non-positive counts are automatically removed

let mut counter = "abbccc".chars().collect::<Counter<_>>();
counter.subtract("abba".chars());
let expect = [('c', 3)].iter().cloned().collect::<HashMap<_, _>>();
assert_eq!(counter.into_map(), expect);

impl<T, N> Counter<T, N> where
    T: Hash + Eq + Clone,
    N: Clone + Ord, 

pub fn most_common(&self) -> Vec<(T, N)>

Create a vector of (elem, frequency) pairs, sorted most to least common.

let mc = "pappaopolo".chars().collect::<Counter<_>>().most_common();
let expected = vec![('p', 4), ('o', 3), ('a', 2), ('l', 1)];
assert_eq!(mc, expected);

Note that the ordering of duplicates is unstable.

pub fn most_common_tiebreaker<F>(&self, tiebreaker: F) -> Vec<(T, N)> where
    F: Fn(&T, &T) -> Ordering, 

Create a vector of (elem, frequency) pairs, sorted most to least common.

In the event that two keys have an equal frequency, use the supplied ordering function to further arrange the results.

For example, we can sort 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_eq!(by_common, expected);

impl<T, N> Counter<T, N> where
    T: Hash + Eq + Clone + Ord,
    N: Clone + Ord, 

pub fn most_common_ordered(&self) -> Vec<(T, N)>

Create a vector of (elem, frequency) pairs, sorted most to least common.

In the event that two keys have an equal frequency, use the natural ordering of the keys to further sort the results.

let mc = "abracadabra".chars().collect::<Counter<_>>().most_common_ordered();
let expect = vec![('a', 5), ('b', 2), ('r', 2), ('c', 1), ('d', 1)];
assert_eq!(mc, expect);

Methods from Deref<Target = HashMap<T, N>>

pub fn capacity(&self) -> usize

Returns the number of elements the map can hold without reallocating.

This number is a lower bound; the HashMap<K, V> might be able to hold more, but is guaranteed to be able to hold at least this many.

Examples

use std::collections::HashMap;
let map: HashMap<i32, i32> = HashMap::with_capacity(100);
assert!(map.capacity() >= 100);

pub fn keys(&self) -> Keys<K, V>

An iterator visiting all keys in arbitrary order. The iterator element type is &'a K.

Examples

use std::collections::HashMap;

let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);

for key in map.keys() {
    println!("{}", key);
}

pub fn values(&self) -> Values<K, V>

An iterator visiting all values in arbitrary order. The iterator element type is &'a V.

Examples

use std::collections::HashMap;

let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);

for val in map.values() {
    println!("{}", val);
}

pub fn values_mut(&mut self) -> ValuesMut<K, V>

An iterator visiting all values mutably in arbitrary order. The iterator element type is &'a mut V.

Examples

use std::collections::HashMap;

let mut map = HashMap::new();

map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);

for val in map.values_mut() {
    *val = *val + 10;
}

for val in map.values() {
    println!("{}", val);
}

pub fn iter(&self) -> Iter<K, V>

An iterator visiting all key-value pairs in arbitrary order. The iterator element type is (&'a K, &'a V).

Examples

use std::collections::HashMap;

let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);

for (key, val) in map.iter() {
    println!("key: {} val: {}", key, val);
}

pub fn iter_mut(&mut self) -> IterMut<K, V>

An iterator visiting all key-value pairs in arbitrary order, with mutable references to the values. The iterator element type is (&'a K, &'a mut V).

Examples

use std::collections::HashMap;

let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);

// Update all values
for (_, val) in map.iter_mut() {
    *val *= 2;
}

for (key, val) in &map {
    println!("key: {} val: {}", key, val);
}

pub fn len(&self) -> usize

Returns the number of elements in the map.

Examples

use std::collections::HashMap;

let mut a = HashMap::new();
assert_eq!(a.len(), 0);
a.insert(1, "a");
assert_eq!(a.len(), 1);

pub fn is_empty(&self) -> bool

Returns true if the map contains no elements.

Examples

use std::collections::HashMap;

let mut a = HashMap::new();
assert!(a.is_empty());
a.insert(1, "a");
assert!(!a.is_empty());

pub fn drain(&mut self) -> Drain<K, V>

Clears the map, returning all key-value pairs as an iterator. Keeps the allocated memory for reuse.

Examples

use std::collections::HashMap;

let mut a = HashMap::new();
a.insert(1, "a");
a.insert(2, "b");

for (k, v) in a.drain().take(1) {
    assert!(k == 1 || k == 2);
    assert!(v == "a" || v == "b");
}

assert!(a.is_empty());

pub fn clear(&mut self)

Clears the map, removing all key-value pairs. Keeps the allocated memory for reuse.

Examples

use std::collections::HashMap;

let mut a = HashMap::new();
a.insert(1, "a");
a.clear();
assert!(a.is_empty());

pub fn hasher(&self) -> &S

Returns a reference to the map's BuildHasher.

Examples

use std::collections::HashMap;
use std::collections::hash_map::RandomState;

let hasher = RandomState::new();
let map: HashMap<i32, i32> = HashMap::with_hasher(hasher);
let hasher: &RandomState = map.hasher();

pub fn reserve(&mut self, additional: usize)

Reserves capacity for at least additional more elements to be inserted in the HashMap. The collection may reserve more space to avoid frequent reallocations.

Panics

Panics if the new allocation size overflows usize.

Examples

use std::collections::HashMap;
let mut map: HashMap<&str, i32> = HashMap::new();
map.reserve(10);

pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError>

🔬 This is a nightly-only experimental API. (try_reserve)

new API

Tries to reserve capacity for at least additional more elements to be inserted in the given HashMap<K,V>. The collection may reserve more space to avoid frequent reallocations.

Errors

If the capacity overflows, or the allocator reports a failure, then an error is returned.

Examples

#![feature(try_reserve)]
use std::collections::HashMap;
let mut map: HashMap<&str, isize> = HashMap::new();
map.try_reserve(10).expect("why is the test harness OOMing on 10 bytes?");

pub fn shrink_to_fit(&mut self)

Shrinks the capacity of the map as much as possible. It will drop down as much as possible while maintaining the internal rules and possibly leaving some space in accordance with the resize policy.

Examples

use std::collections::HashMap;

let mut map: HashMap<i32, i32> = HashMap::with_capacity(100);
map.insert(1, 2);
map.insert(3, 4);
assert!(map.capacity() >= 100);
map.shrink_to_fit();
assert!(map.capacity() >= 2);

pub fn shrink_to(&mut self, min_capacity: usize)

🔬 This is a nightly-only experimental API. (shrink_to)

new API

Shrinks the capacity of the map with a lower limit. It will drop down no lower than the supplied limit while maintaining the internal rules and possibly leaving some space in accordance with the resize policy.

Panics if the current capacity is smaller than the supplied minimum capacity.

Examples

#![feature(shrink_to)]
use std::collections::HashMap;

let mut map: HashMap<i32, i32> = HashMap::with_capacity(100);
map.insert(1, 2);
map.insert(3, 4);
assert!(map.capacity() >= 100);
map.shrink_to(10);
assert!(map.capacity() >= 10);
map.shrink_to(0);
assert!(map.capacity() >= 2);

pub fn entry(&mut self, key: K) -> Entry<K, V>

Gets the given key's corresponding entry in the map for in-place manipulation.

Examples

use std::collections::HashMap;

let mut letters = HashMap::new();

for ch in "a short treatise on fungi".chars() {
    let counter = letters.entry(ch).or_insert(0);
    *counter += 1;
}

assert_eq!(letters[&'s'], 2);
assert_eq!(letters[&'t'], 3);
assert_eq!(letters[&'u'], 1);
assert_eq!(letters.get(&'y'), None);

pub fn get<Q>(&self, k: &Q) -> Option<&V> where
    K: Borrow<Q>,
    Q: Hash + Eq + ?Sized, 

Returns a reference to the value corresponding to the key.

The key may be any borrowed form of the map's key type, but Hash and Eq on the borrowed form must match those for the key type.

Examples

use std::collections::HashMap;

let mut map = HashMap::new();
map.insert(1, "a");
assert_eq!(map.get(&1), Some(&"a"));
assert_eq!(map.get(&2), None);

pub fn get_key_value<Q>(&self, k: &Q) -> Option<(&K, &V)> where
    K: Borrow<Q>,
    Q: Hash + Eq + ?Sized, 

Returns the key-value pair corresponding to the supplied key.

The supplied key may be any borrowed form of the map's key type, but Hash and Eq on the borrowed form must match those for the key type.

Examples

use std::collections::HashMap;

let mut map = HashMap::new();
map.insert(1, "a");
assert_eq!(map.get_key_value(&1), Some((&1, &"a")));
assert_eq!(map.get_key_value(&2), None);

pub fn contains_key<Q>(&self, k: &Q) -> bool where
    K: Borrow<Q>,
    Q: Hash + Eq + ?Sized, 

Returns true if the map contains a value for the specified key.

The key may be any borrowed form of the map's key type, but Hash and Eq on the borrowed form must match those for the key type.

Examples

use std::collections::HashMap;

let mut map = HashMap::new();
map.insert(1, "a");
assert_eq!(map.contains_key(&1), true);
assert_eq!(map.contains_key(&2), false);

pub fn get_mut<Q>(&mut self, k: &Q) -> Option<&mut V> where
    K: Borrow<Q>,
    Q: Hash + Eq + ?Sized, 

Returns a mutable reference to the value corresponding to the key.

The key may be any borrowed form of the map's key type, but Hash and Eq on the borrowed form must match those for the key type.

Examples

use std::collections::HashMap;

let mut map = HashMap::new();
map.insert(1, "a");
if let Some(x) = map.get_mut(&1) {
    *x = "b";
}
assert_eq!(map[&1], "b");

pub fn insert(&mut self, k: K, v: V) -> Option<V>

Inserts a key-value pair into the map.

If the map did not have this key present, None is returned.

If the map did have this key present, the value is updated, and the old value is returned. The key is not updated, though; this matters for types that can be == without being identical. See the module-level documentation for more.

Examples

use std::collections::HashMap;

let mut map = HashMap::new();
assert_eq!(map.insert(37, "a"), None);
assert_eq!(map.is_empty(), false);

map.insert(37, "b");
assert_eq!(map.insert(37, "c"), Some("b"));
assert_eq!(map[&37], "c");

pub fn remove<Q>(&mut self, k: &Q) -> Option<V> where
    K: Borrow<Q>,
    Q: Hash + Eq + ?Sized, 

Removes a key from the map, returning the value at the key if the key was previously in the map.

The key may be any borrowed form of the map's key type, but Hash and Eq on the borrowed form must match those for the key type.

Examples

use std::collections::HashMap;

let mut map = HashMap::new();
map.insert(1, "a");
assert_eq!(map.remove(&1), Some("a"));
assert_eq!(map.remove(&1), None);

pub fn remove_entry<Q>(&mut self, k: &Q) -> Option<(K, V)> where
    K: Borrow<Q>,
    Q: Hash + Eq + ?Sized, 

Removes a key from the map, returning the stored key and value if the key was previously in the map.

The key may be any borrowed form of the map's key type, but Hash and Eq on the borrowed form must match those for the key type.

Examples

use std::collections::HashMap;

let mut map = HashMap::new();
map.insert(1, "a");
assert_eq!(map.remove_entry(&1), Some((1, "a")));
assert_eq!(map.remove(&1), None);

pub fn retain<F>(&mut self, f: F) where
    F: FnMut(&K, &mut V) -> bool, 

Retains only the elements specified by the predicate.

In other words, remove all pairs (k, v) such that f(&k,&mut v) returns false.

Examples

use std::collections::HashMap;

let mut map: HashMap<i32, i32> = (0..8).map(|x|(x, x*10)).collect();
map.retain(|&k, _| k % 2 == 0);
assert_eq!(map.len(), 4);

pub fn raw_entry_mut(&mut self) -> RawEntryBuilderMut<K, V, S>

🔬 This is a nightly-only experimental API. (hash_raw_entry)

Creates a raw entry builder for the HashMap.

Raw entries provide the lowest level of control for searching and manipulating a map. They must be manually initialized with a hash and then manually searched. After this, insertions into a vacant entry still require an owned key to be provided.

Raw entries are useful for such exotic situations as:

• Hash memoization
• Deferring the creation of an owned key until it is known to be required
• Using a search key that doesn't work with the Borrow trait
• Using custom comparison logic without newtype wrappers

Because raw entries provide much more low-level control, it's much easier to put the HashMap into an inconsistent state which, while memory-safe, will cause the map to produce seemingly random results. Higher-level and more foolproof APIs like entry should be preferred when possible.

In particular, the hash used to initialized the raw entry must still be consistent with the hash of the key that is ultimately stored in the entry. This is because implementations of HashMap may need to recompute hashes when resizing, at which point only the keys are available.

Raw entries give mutable access to the keys. This must not be used to modify how the key would compare or hash, as the map will not re-evaluate where the key should go, meaning the keys may become "lost" if their location does not reflect their state. For instance, if you change a key so that the map now contains keys which compare equal, search may start acting erratically, with two keys randomly masking each other. Implementations are free to assume this doesn't happen (within the limits of memory-safety).

pub fn raw_entry(&self) -> RawEntryBuilder<K, V, S>

🔬 This is a nightly-only experimental API. (hash_raw_entry)

Creates a raw immutable entry builder for the HashMap.

Raw entries provide the lowest level of control for searching and manipulating a map. They must be manually initialized with a hash and then manually searched.

This is useful for

• Hash memoization
• Using a search key that doesn't work with the Borrow trait
• Using custom comparison logic without newtype wrappers

Unless you are in such a situation, higher-level and more foolproof APIs like get should be preferred.

Immutable raw entries have very limited use; you might instead want raw_entry_mut.

Trait Implementations

impl<T, N> Add<Counter<T, N>> for Counter<T, N> where
    T: Clone + Hash + Eq,
    N: Clone + PartialOrd + PartialEq + AddAssign + Zero, 

type Output = Counter<T, N>

The resulting type after applying the + operator.

fn add(self, rhs: Counter<T, N>) -> Self::Output

Add two counters together.

out = c + d; -> out[x] == c[x] + d[x] for all x

let c = "aaab".chars().collect::<Counter<_>>();
let d = "abb".chars().collect::<Counter<_>>();

let e = c + d;

let expect = [('a', 4), ('b', 3)].iter().cloned().collect::<HashMap<_, _>>();
assert_eq!(e.into_map(), expect);

impl<I, T, N> Add<I> for Counter<T, N> where
    I: IntoIterator<Item = T>,
    T: Hash + Eq,
    N: PartialOrd + AddAssign + SubAssign + Zero + One, 

type Output = Self

The resulting type after applying the + operator.

fn add(self, rhs: I) -> Self::Output

Consume self producing a Counter like self updated with the counts of the elements of I.

let counter = Counter::init("abbccc".chars());

let new_counter = counter + "aeeeee".chars();
let expected: HashMap<char, usize> = [('a', 2), ('b', 2), ('c', 3), ('e', 5)]
    .iter().cloned().collect();
assert_eq!(new_counter.into_map(), expected);

impl<T, N> AddAssign<Counter<T, N>> for Counter<T, N> where
    T: Clone + Hash + Eq,
    N: Clone + Zero + AddAssign, 

fn add_assign(&mut self, rhs: Self)

Add another counter to this counter

c += d; -> c[x] += d[x] for all x

let mut c = "aaab".chars().collect::<Counter<_>>();
let d = "abb".chars().collect::<Counter<_>>();

c += d;

let expect = [('a', 4), ('b', 3)].iter().cloned().collect::<HashMap<_, _>>();
assert_eq!(c.into_map(), expect);

impl<I, T, N> AddAssign<I> for Counter<T, N> where
    I: IntoIterator<Item = T>,
    T: Hash + Eq,
    N: PartialOrd + AddAssign + SubAssign + Zero + One, 

fn add_assign(&mut self, rhs: I)

Directly add the counts of the elements of I to self

let mut counter = Counter::init("abbccc".chars());

counter += "aeeeee".chars();
let expected: HashMap<char, usize> = [('a', 2), ('b', 2), ('c', 3), ('e', 5)]
    .iter().cloned().collect();
assert_eq!(counter.into_map(), expected);

impl<T, N> BitAnd<Counter<T, N>> for Counter<T, N> where
    T: Clone + Hash + Eq,
    N: Clone + Ord + AddAssign + SubAssign + Zero + One, 

type Output = Counter<T, N>

The resulting type after applying the & operator.

fn bitand(self, rhs: Counter<T, N>) -> Self::Output

Intersection

out = c & d; -> out[x] == min(c[x], d[x])

let c = "aaab".chars().collect::<Counter<_>>();
let d = "abb".chars().collect::<Counter<_>>();

let e = c & d;

let expect = [('a', 1), ('b', 1)].iter().cloned().collect::<HashMap<_, _>>();
assert_eq!(e.into_map(), expect);

impl<T, N> BitOr<Counter<T, N>> for Counter<T, N> where
    T: Clone + Hash + Eq,
    N: Clone + Ord + Zero, 

type Output = Counter<T, N>

The resulting type after applying the | operator.

fn bitor(self, rhs: Counter<T, N>) -> Self::Output

Union

out = c | d; -> out[x] == max(c[x], d[x])

let c = "aaab".chars().collect::<Counter<_>>();
let d = "abb".chars().collect::<Counter<_>>();

let e = c | d;

let expect = [('a', 3), ('b', 2)].iter().cloned().collect::<HashMap<_, _>>();
assert_eq!(e.into_map(), expect);

impl<T: Clone + Hash + Eq, N: Clone> Clone for Counter<T, N>

fn clone(&self) -> Counter<T, N>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Debug + Hash + Eq, N: Debug> Debug for Counter<T, N>

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl<T: Default + Hash + Eq, N: Default> Default for Counter<T, N>

fn default() -> Counter<T, N>

Returns the "default value" for a type.

impl<T, N> Deref for Counter<T, N> where
    T: Hash + Eq,
    N: Clone, 

type Target = HashMap<T, N>

The resulting type after dereferencing.

fn deref(&self) -> &HashMap<T, N>

Dereferences the value.

impl<T, N> DerefMut for Counter<T, N> where
    T: Hash + Eq,
    N: Clone, 

fn deref_mut(&mut self) -> &mut HashMap<T, N>

Mutably dereferences the value.

impl<T: Eq + Hash, N: Eq> Eq for Counter<T, N>

impl<T, N> FromIterator<(T, N)> for Counter<T, N> where
    T: Hash + Eq,
    N: PartialOrd + AddAssign + SubAssign + Zero + One, 

fn from_iter<I: IntoIterator<Item = (T, N)>>(iter: I) -> Self

from_iter creates a counter from (item, count) tuples.

The counts of duplicate items are summed.

let counter = [('a', 1), ('b', 2), ('c', 3), ('a', 4)].iter()
    .cloned().collect::<Counter<_>>();
let expect = [('a', 5), ('b', 2), ('c', 3)].iter()
    .cloned().collect::<HashMap<_, _>>();
assert_eq!(counter.into_map(), expect);

impl<T, N> FromIterator<T> for Counter<T, N> where
    T: Hash + Eq,
    N: PartialOrd + AddAssign + SubAssign + Zero + One, 

fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self

Produce a Counter from an iterator of items. This is called automatically by iter.collect().

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

impl<'_, T, Q, N> Index<&'_ Q> for Counter<T, N> where
    T: Hash + Eq + Borrow<Q>,
    Q: Hash + Eq,
    N: Zero, 

type Output = N

The returned type after indexing.

fn index(&self, key: &Q) -> &N

Index in immutable contexts

Returns a reference to a zero value for missing keys.

let counter = Counter::<_>::init("aabbcc".chars());
assert_eq!(counter[&'a'], 2);
assert_eq!(counter[&'b'], 2);
assert_eq!(counter[&'c'], 2);
assert_eq!(counter[&'d'], 0);

Note that the zero is a struct filed but not one of the values of the inner HashMap. This method does not modify any existing value.

let counter = Counter::<_>::init("".chars());
assert_eq!(counter[&'a'], 0);
assert_eq!(counter.get(&'a'), None); // as `Deref<Target = HashMap<_, _>>`

impl<'_, T, Q, N> IndexMut<&'_ Q> for Counter<T, N> where
    T: Hash + Eq + Borrow<Q>,
    Q: Hash + Eq + ToOwned<Owned = T>,
    N: Zero, 

fn index_mut(&mut self, key: &Q) -> &mut N

Index in mutable contexts

If the given key is not present, creates a new entry and initializes it with a zero value.

let mut counter = Counter::<_>::init("aabbcc".chars());
counter[&'c'] += 1;
counter[&'d'] += 1;
assert_eq!(counter[&'c'], 3);
assert_eq!(counter[&'d'], 1);

Unlike Index::index, The returned mutable reference to the zero is actually one of the values of the inner HashMap.

let mut counter = Counter::<_>::init("".chars());
assert_eq!(counter.get(&'a'), None); // as `Deref<Target = HashMap<_, _>>`
let _ = &mut counter[&'a'];
assert_eq!(counter.get(&'a'), Some(&0));

impl<T: PartialEq + Hash + Eq, N: PartialEq> PartialEq<Counter<T, N>> for Counter<T, N>

fn eq(&self, other: &Counter<T, N>) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Counter<T, N>) -> bool

This method tests for !=.

impl<T: Hash + Eq, N> StructuralEq for Counter<T, N>

impl<T: Hash + Eq, N> StructuralPartialEq for Counter<T, N>

impl<T, N> Sub<Counter<T, N>> for Counter<T, N> where
    T: Hash + Eq,
    N: Clone + PartialOrd + PartialEq + SubAssign + Zero, 

type Output = Counter<T, N>

The resulting type after applying the - operator.

fn sub(self, rhs: Counter<T, N>) -> Self::Output

Subtract (keeping only positive values).

out = c - d; -> out[x] == c[x] - d[x] for all x, keeping only items with a value greater than N::zero().

let c = "aaab".chars().collect::<Counter<_>>();
let d = "abb".chars().collect::<Counter<_>>();

let e = c - d;

let expect = [('a', 2)].iter().cloned().collect::<HashMap<_, _>>();
assert_eq!(e.into_map(), expect);

impl<I, T, N> Sub<I> for Counter<T, N> where
    I: IntoIterator<Item = T>,
    T: Clone + Hash + Eq,
    N: Clone + PartialOrd + AddAssign + SubAssign + Zero + One, 

type Output = Self

The resulting type after applying the - operator.

fn sub(self, rhs: I) -> Self::Output

Consume self producing a Counter like self with the counts of the elements of I subtracted, keeping only positive values.

let c = "aaab".chars().collect::<Counter<_>>();
let e = c - "abb".chars();

let expect = [('a', 2)].iter().cloned().collect::<HashMap<_, _>>();
assert_eq!(e.into_map(), expect);

impl<T, N> SubAssign<Counter<T, N>> for Counter<T, N> where
    T: Hash + Eq,
    N: Clone + PartialOrd + PartialEq + SubAssign + Zero, 

fn sub_assign(&mut self, rhs: Self)

Subtract (keeping only positive values).

c -= d; -> c[x] -= d[x] for all x, keeping only items with a value greater than N::zero().

let mut c = "aaab".chars().collect::<Counter<_>>();
let d = "abb".chars().collect::<Counter<_>>();

c -= d;

let expect = [('a', 2)].iter().cloned().collect::<HashMap<_, _>>();
assert_eq!(c.into_map(), expect);

impl<I, T, N> SubAssign<I> for Counter<T, N> where
    I: IntoIterator<Item = T>,
    T: Hash + Eq,
    N: PartialOrd + AddAssign + SubAssign + Zero + One, 

fn sub_assign(&mut self, rhs: I)

Directly subtract the counts of the elements of I from self, keeping only items with a value greater than N::zero().

let mut c = "aaab".chars().collect::<Counter<_>>();
c -= "abb".chars();

let expect = [('a', 2)].iter().cloned().collect::<HashMap<_, _>>();
assert_eq!(c.into_map(), expect);