Struct indexmap::map::IndexMap

pub struct IndexMap<K, V, S = RandomState> { /* fields omitted */ }

A hash table where the iteration order of the key-value pairs is independent of the hash values of the keys.

The interface is closely compatible with the standard HashMap, but also has additional features.

Order

The key-value pairs have a consistent order that is determined by the sequence of insertion and removal calls on the map. The order does not depend on the keys or the hash function at all.

All iterators traverse the map in the order.

The insertion order is preserved, with notable exceptions like the .remove() or .swap_remove() methods. Methods such as .sort_by() of course result in a new order, depending on the sorting order.

Indices

The key-value pairs are indexed in a compact range without holes in the range 0..self.len(). For example, the method .get_full looks up the index for a key, and the method .get_index looks up the key-value pair by index.

Examples

use indexmap::IndexMap;

// count the frequency of each letter in a sentence.
let mut letters = IndexMap::new();
for ch in "a short treatise on fungi".chars() {
    *letters.entry(ch).or_insert(0) += 1;
}
 
assert_eq!(letters[&'s'], 2);
assert_eq!(letters[&'t'], 3);
assert_eq!(letters[&'u'], 1);
assert_eq!(letters.get(&'y'), None);

Methods

impl<K, V> IndexMap<K, V>

pub fn new() -> Self

Create a new map. (Does not allocate.)

pub fn with_capacity(n: usize) -> Self

Create a new map with capacity for n key-value pairs. (Does not allocate if n is zero.)

Computes in O(n) time.

impl<K, V, S> IndexMap<K, V, S>

pub fn with_capacity_and_hasher(n: usize, hash_builder: S) -> Self where
    S: BuildHasher, 

Create a new map with capacity for n key-value pairs. (Does not allocate if n is zero.)

Computes in O(n) time.

pub fn len(&self) -> usize

Return the number of key-value pairs in the map.

Computes in O(1) time.

pub fn is_empty(&self) -> bool

Returns true if the map contains no elements.

Computes in O(1) time.

pub fn with_hasher(hash_builder: S) -> Self where
    S: BuildHasher, 

Create a new map with hash_builder

pub fn hasher(&self) -> &S where
    S: BuildHasher, 

Return a reference to the map's BuildHasher.

pub fn capacity(&self) -> usize

Computes in O(1) time.

impl<K, V, S> IndexMap<K, V, S> where
    K: Hash + Eq,
    S: BuildHasher, 

pub fn clear(&mut self)

Remove all key-value pairs in the map, while preserving its capacity.

Computes in O(n) time.

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

Reserve capacity for additional more key-value pairs.

FIXME Not implemented fully yet.

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

Insert a key-value pair in the map.

If an equivalent key already exists in the map: the key remains and retains in its place in the order, its corresponding value is updated with value and the older value is returned inside Some(_).

If no equivalent key existed in the map: the new key-value pair is inserted, last in order, and None is returned.

Computes in O(1) time (amortized average).

See also entry if you you want to insert or modify or if you need to get the index of the corresponding key-value pair.

pub fn insert_full(&mut self, key: K, value: V) -> (usize, Option<V>)

Insert a key-value pair in the map, and get their index.

If an equivalent key already exists in the map: the key remains and retains in its place in the order, its corresponding value is updated with value and the older value is returned inside (index, Some(_)).

If no equivalent key existed in the map: the new key-value pair is inserted, last in order, and (index, None) is returned.

Computes in O(1) time (amortized average).

See also entry if you you want to insert or modify or if you need to get the index of the corresponding key-value pair.

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

Get the given key’s corresponding entry in the map for insertion and/or in-place manipulation.

Computes in O(1) time (amortized average).

Important traits for Iter<'a, K, V>

impl<'a, K, V> Iterator for Iter<'a, K, V> type Item = (&'a K, &'a V);

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

Return an iterator over the key-value pairs of the map, in their order

Important traits for IterMut<'a, K, V>

impl<'a, K, V> Iterator for IterMut<'a, K, V> type Item = (&'a K, &'a mut V);

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

Return an iterator over the key-value pairs of the map, in their order

Important traits for Keys<'a, K, V>

impl<'a, K, V> Iterator for Keys<'a, K, V> type Item = &'a K;

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

Return an iterator over the keys of the map, in their order

Important traits for Values<'a, K, V>

impl<'a, K, V> Iterator for Values<'a, K, V> type Item = &'a V;

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

Return an iterator over the values of the map, in their order

Important traits for ValuesMut<'a, K, V>

impl<'a, K, V> Iterator for ValuesMut<'a, K, V> type Item = &'a mut V;

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

Return an iterator over mutable references to the the values of the map, in their order

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

Return true if an equivalent to key exists in the map.

Computes in O(1) time (average).

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

Return a reference to the value stored for key, if it is present, else None.

Computes in O(1) time (average).

pub fn get_full<Q: ?Sized>(&self, key: &Q) -> Option<(usize, &K, &V)> where
    Q: Hash + Equivalent<K>, 

Return item index, key and value

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

pub fn get_full_mut<Q: ?Sized>(
    &mut self,
    key: &Q
) -> Option<(usize, &K, &mut V)> where
    Q: Hash + Equivalent<K>, 

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

Remove the key-value pair equivalent to key and return its value.

NOTE: This is equivalent to .swap_remove(key), if you need to preserve the order of the keys in the map, use .shift_remove(key) instead.

Computes in O(1) time (average).

pub fn swap_remove<Q: ?Sized>(&mut self, key: &Q) -> Option<V> where
    Q: Hash + Equivalent<K>, 

Remove the key-value pair equivalent to key and return its value.

Like Vec::swap_remove, the pair is removed by swapping it with the last element of the map and popping it off. This perturbs the postion of what used to be the last element!

Return None if key is not in map.

Computes in O(1) time (average).

pub fn swap_remove_full<Q: ?Sized>(&mut self, key: &Q) -> Option<(usize, K, V)> where
    Q: Hash + Equivalent<K>, 

Remove the key-value pair equivalent to key and return it and the index it had.

Like Vec::swap_remove, the pair is removed by swapping it with the last element of the map and popping it off. This perturbs the postion of what used to be the last element!

Return None if key is not in map.

Computes in O(1) time (average).

pub fn shift_remove<Q: ?Sized>(&mut self, key: &Q) -> Option<V> where
    Q: Hash + Equivalent<K>, 

Remove the key-value pair equivalent to key and return its value.

Like Vec::remove, the pair is removed by shifting all of the elements that follow it, preserving their relative order. This perturbs the index of all of those elements!

Return None if key is not in map.

Computes in O(n) time (average).

pub fn shift_remove_full<Q: ?Sized>(&mut self, key: &Q) -> Option<(usize, K, V)> where
    Q: Hash + Equivalent<K>, 

Remove the key-value pair equivalent to key and return it and the index it had.

Like Vec::remove, the pair is removed by shifting all of the elements that follow it, preserving their relative order. This perturbs the index of all of those elements!

Return None if key is not in map.

Computes in O(n) time (average).

pub fn pop(&mut self) -> Option<(K, V)>

Remove the last key-value pair

Computes in O(1) time (average).

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

Scan through each key-value pair in the map and keep those where the closure keep returns true.

The elements are visited in order, and remaining elements keep their order.

Computes in O(n) time (average).

pub fn sort_keys(&mut self) where
    K: Ord, 

Sort the map’s key-value pairs by the default ordering of the keys.

See sort_by for details.

pub fn sort_by<F>(&mut self, compare: F) where
    F: FnMut(&K, &V, &K, &V) -> Ordering, 

Sort the map’s key-value pairs in place using the comparison function compare.

The comparison function receives two key and value pairs to compare (you can sort by keys or values or their combination as needed).

Computes in O(n log n + c) time and O(n) space where n is the length of the map and c the capacity. The sort is stable.

Important traits for IntoIter<K, V>

impl<K, V> Iterator for IntoIter<K, V> type Item = (K, V);

pub fn sorted_by<F>(self, cmp: F) -> IntoIter<K, V> where
    F: FnMut(&K, &V, &K, &V) -> Ordering, 

Sort the key-value pairs of the map and return a by value iterator of the key-value pairs with the result.

The sort is stable.

Important traits for Drain<'a, K, V>

impl<'a, K, V> Iterator for Drain<'a, K, V> type Item = (K, V);

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

Clears the IndexMap, returning all key-value pairs as a drain iterator. Keeps the allocated memory for reuse.

impl<K, V, S> IndexMap<K, V, S>

pub fn get_index(&self, index: usize) -> Option<(&K, &V)>

Get a key-value pair by index

Valid indices are 0 <= index < self.len()

Computes in O(1) time.

pub fn get_index_mut(&mut self, index: usize) -> Option<(&mut K, &mut V)>

Get a key-value pair by index

Valid indices are 0 <= index < self.len()

Computes in O(1) time.

pub fn swap_remove_index(&mut self, index: usize) -> Option<(K, V)>

Remove the key-value pair by index

Valid indices are 0 <= index < self.len()

Like Vec::swap_remove, the pair is removed by swapping it with the last element of the map and popping it off. This perturbs the postion of what used to be the last element!

Computes in O(1) time (average).

pub fn shift_remove_index(&mut self, index: usize) -> Option<(K, V)>

Remove the key-value pair by index

Valid indices are 0 <= index < self.len()

Like Vec::remove, the pair is removed by shifting all of the elements that follow it, preserving their relative order. This perturbs the index of all of those elements!

Computes in O(n) time (average).

Trait Implementations

impl<K, V, S> MutableKeys for IndexMap<K, V, S> where
    K: Eq + Hash,
    S: BuildHasher, 

Opt-in mutable access to keys.

See MutableKeys for more information.

type Key = K

type Value = V

fn get_full_mut2<Q: ?Sized>(
    &mut self,
    key: &Q
) -> Option<(usize, &mut K, &mut V)> where
    Q: Hash + Equivalent<K>, 

Return item index, mutable reference to key and value

fn retain2<F>(&mut self, keep: F) where
    F: FnMut(&mut K, &mut V) -> bool, 

Scan through each key-value pair in the map and keep those where the closure keep returns true.

fn __private_marker(&self) -> PrivateMarker

This method is not useful in itself – it is there to “seal” the trait for external implementation, so that we can add methods without causing breaking changes.

impl<K, V, S> Eq for IndexMap<K, V, S> where
    K: Eq + Hash,
    V: Eq,
    S: BuildHasher, 

impl<K, V, S> Default for IndexMap<K, V, S> where
    S: BuildHasher + Default, 

fn default() -> Self

Return an empty IndexMap

impl<K: Clone, V: Clone, S: Clone> Clone for IndexMap<K, V, S>

fn clone(&self) -> IndexMap<K, V, S>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<K, V, S> Extend<(K, V)> for IndexMap<K, V, S> where
    K: Hash + Eq,
    S: BuildHasher, 

fn extend<I: IntoIterator<Item = (K, V)>>(&mut self, iterable: I)

Extend the map with all key-value pairs in the iterable.

This is equivalent to calling insert for each of them in order, which means that for keys that already existed in the map, their value is updated but it keeps the existing order.

New keys are inserted in the order they appear in the sequence. If equivalents of a key occur more than once, the last corresponding value prevails.

impl<'a, K, V, S> Extend<(&'a K, &'a V)> for IndexMap<K, V, S> where
    K: Hash + Eq + Copy,
    V: Copy,
    S: BuildHasher, 

fn extend<I: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iterable: I)

Extend the map with all key-value pairs in the iterable.

See the first extend method for more details.

impl<K, V1, S1, V2, S2> PartialEq<IndexMap<K, V2, S2>> for IndexMap<K, V1, S1> where
    K: Hash + Eq,
    V1: PartialEq<V2>,
    S1: BuildHasher,
    S2: BuildHasher, 

fn eq(&self, other: &IndexMap<K, V2, S2>) -> bool

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

#[must_use] fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl<'a, K, V, S> IntoIterator for &'a IndexMap<K, V, S> where
    K: Hash + Eq,
    S: BuildHasher, 

type Item = (&'a K, &'a V)

The type of the elements being iterated over.

type IntoIter = Iter<'a, K, V>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<'a, K, V, S> IntoIterator for &'a mut IndexMap<K, V, S> where
    K: Hash + Eq,
    S: BuildHasher, 

type Item = (&'a K, &'a mut V)

The type of the elements being iterated over.

type IntoIter = IterMut<'a, K, V>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<K, V, S> IntoIterator for IndexMap<K, V, S> where
    K: Hash + Eq,
    S: BuildHasher, 

type Item = (K, V)

The type of the elements being iterated over.

type IntoIter = IntoIter<K, V>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<'a, K, V, Q: ?Sized, S> Index<&'a Q> for IndexMap<K, V, S> where
    Q: Hash + Equivalent<K>,
    K: Hash + Eq,
    S: BuildHasher, 

type Output = V

The returned type after indexing.

fn index(&self, key: &'a Q) -> &V

Panics if key is not present in the map.

impl<'a, K, V, Q: ?Sized, S> IndexMut<&'a Q> for IndexMap<K, V, S> where
    Q: Hash + Equivalent<K>,
    K: Hash + Eq,
    S: BuildHasher, 

Mutable indexing allows changing / updating values of key-value pairs that are already present.

You can not insert new pairs with index syntax, use .insert().

fn index_mut(&mut self, key: &'a Q) -> &mut V

Panics if key is not present in the map.

impl<K, V, S> Debug for IndexMap<K, V, S> where
    K: Debug + Hash + Eq,
    V: Debug,
    S: BuildHasher, 

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

Formats the value using the given formatter.

impl<K, V, S> FromIterator<(K, V)> for IndexMap<K, V, S> where
    K: Hash + Eq,
    S: BuildHasher + Default, 

fn from_iter<I: IntoIterator<Item = (K, V)>>(iterable: I) -> Self

Create an IndexMap from the sequence of key-value pairs in the iterable.

from_iter uses the same logic as extend. See extend for more details.