Struct IndexMap

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

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);

Implementations

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

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

Computes in O(n) time.

pub const fn with_hasher(hash_builder: S) -> Self

Create a new map with hash_builder.

This function is const, so it can be called in static contexts.

pub fn capacity(&self) -> usize

Computes in O(1) time.

pub fn hasher(&self) -> &S

Return a reference to the map’s BuildHasher.

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 iter(&self) -> Iter<'_, K, V>

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

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

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

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

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

pub fn into_keys(self) -> IntoKeys<K, V>

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

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

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

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

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

pub fn into_values(self) -> IntoValues<K, V>

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

pub fn clear(&mut self)

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

Computes in O(n) time.

pub fn truncate(&mut self, len: usize)

Shortens the map, keeping the first len elements and dropping the rest.

If len is greater than the map’s current length, this has no effect.

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

where R: RangeBounds<usize>,

Clears the IndexMap in the given index range, returning those key-value pairs as a drain iterator.

The range may be any type that implements RangeBounds<usize>, including all of the std::ops::Range* types, or even a tuple pair of Bound start and end values. To drain the map entirely, use RangeFull like map.drain(..).

This shifts down all entries following the drained range to fill the gap, and keeps the allocated memory for reuse.

Panics if the starting point is greater than the end point or if the end point is greater than the length of the map.

pub fn split_off(&mut self, at: usize) -> Self

where S: Clone,

Splits the collection into two at the given index.

Returns a newly allocated map containing the elements in the range [at, len). After the call, the original map will be left containing the elements [0, at) with its previous capacity unchanged.

Panics if at > len.

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

where K: Hash + Eq, S: BuildHasher,

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

Reserve capacity for additional more key-value pairs.

Computes in O(n) time.

pub fn shrink_to_fit(&mut self)

Shrink the capacity of the map as much as possible.

Computes in O(n) time.

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

Shrink the capacity of the map with a lower limit.

Computes in O(n) time.

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).

pub fn contains_key<Q>(&self, key: &Q) -> bool

where Q: Hash + Equivalent<K> + ?Sized,

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

Computes in O(1) time (average).

pub fn get<Q>(&self, key: &Q) -> Option<&V>

where Q: Hash + Equivalent<K> + ?Sized,

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

Computes in O(1) time (average).

pub fn get_key_value<Q>(&self, key: &Q) -> Option<(&K, &V)>

where Q: Hash + Equivalent<K> + ?Sized,

Return references to the key-value pair stored for key, if it is present, else None.

Computes in O(1) time (average).

pub fn get_full<Q>(&self, key: &Q) -> Option<(usize, &K, &V)>

where Q: Hash + Equivalent<K> + ?Sized,

Return item index, key and value

pub fn get_index_of<Q>(&self, key: &Q) -> Option<usize>

where Q: Hash + Equivalent<K> + ?Sized,

Return item index, if it exists in the map

Computes in O(1) time (average).

pub fn get_mut<Q>(&mut self, key: &Q) -> Option<&mut V>

where Q: Hash + Equivalent<K> + ?Sized,

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

where Q: Hash + Equivalent<K> + ?Sized,

pub fn remove<Q>(&mut self, key: &Q) -> Option<V>

where Q: Hash + Equivalent<K> + ?Sized,

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 remove_entry<Q>(&mut self, key: &Q) -> Option<(K, V)>

where Q: Hash + Equivalent<K> + ?Sized,

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

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

Computes in O(1) time (average).

pub fn swap_remove<Q>(&mut self, key: &Q) -> Option<V>

where Q: Hash + Equivalent<K> + ?Sized,

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 position 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_entry<Q>(&mut self, key: &Q) -> Option<(K, V)>

where Q: Hash + Equivalent<K> + ?Sized,

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

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 position 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>(&mut self, key: &Q) -> Option<(usize, K, V)>

where Q: Hash + Equivalent<K> + ?Sized,

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 position 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>(&mut self, key: &Q) -> Option<V>

where Q: Hash + Equivalent<K> + ?Sized,

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_entry<Q>(&mut self, key: &Q) -> Option<(K, V)>

where Q: Hash + Equivalent<K> + ?Sized,

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

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>(&mut self, key: &Q) -> Option<(usize, K, V)>

where Q: Hash + Equivalent<K> + ?Sized,

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

This preserves the order of the remaining elements.

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, cmp: F)

where F: FnMut(&K, &V, &K, &V) -> Ordering,

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

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.

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.

pub fn sort_unstable_keys(&mut self)

where K: Ord,

Sort the map’s key-value pairs by the default ordering of the keys, but may not preserve the order of equal elements.

See sort_unstable_by for details.

pub fn sort_unstable_by<F>(&mut self, cmp: F)

where F: FnMut(&K, &V, &K, &V) -> Ordering,

Sort the map’s key-value pairs in place using the comparison function cmp, but may not preserve the order of equal elements.

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 where n is the length of the map and c is the capacity. The sort is unstable.

pub fn sorted_unstable_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 unstable.

pub fn reverse(&mut self)

Reverses the order of the map’s key-value pairs in place.

Computes in O(n) time and O(1) space.

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 first(&self) -> Option<(&K, &V)>

Get the first key-value pair

Computes in O(1) time.

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

Get the first key-value pair, with mutable access to the value

Computes in O(1) time.

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

Get the last key-value pair

Computes in O(1) time.

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

Get the last key-value pair, with mutable access to the value

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 position 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).

pub fn move_index(&mut self, from: usize, to: usize)

Moves the position of a key-value pair from one index to another by shifting all other pairs in-between.

• If from < to, the other pairs will shift down while the targeted pair moves up.
• If from > to, the other pairs will shift up while the targeted pair moves down.

Panics if from or to are out of bounds.

Computes in O(n) time (average).

pub fn swap_indices(&mut self, a: usize, b: usize)

Swaps the position of two key-value pairs in the map.

Panics if a or b are out of bounds.

Trait Implementations

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

where K: Clone, V: Clone, S: Clone,

fn clone(&self) -> Self

Returns a copy of the value.

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

Performs copy-assignment from source.

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

where K: Debug, V: Debug,

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

Formats the value using the given formatter.

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

where S: Default,

fn default() -> Self

Return an empty IndexMap

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.

fn extend_one(&mut self, item: A)

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

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

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

Reserves capacity in a collection for the given number of additional elements.

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.

fn extend_one(&mut self, item: A)

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

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

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

Reserves capacity in a collection for the given number of additional elements.

impl<K, V, const N: usize> From<[(K, V); N]> for IndexMap<K, V, RandomState>

where K: Hash + Eq,

fn from(arr: [(K, V); N]) -> Self

Examples

use indexmap::IndexMap;

let map1 = IndexMap::from([(1, 2), (3, 4)]);
let map2: IndexMap<_, _> = [(1, 2), (3, 4)].into();
assert_eq!(map1, map2);

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.

impl<K, V, Q, S> Index<&Q> for IndexMap<K, V, S>

where Q: Hash + Equivalent<K> + ?Sized, K: Hash + Eq, S: BuildHasher,

Access IndexMap values corresponding to a key.

Examples

use indexmap::IndexMap;

let mut map = IndexMap::new();
for word in "Lorem ipsum dolor sit amet".split_whitespace() {
    map.insert(word.to_lowercase(), word.to_uppercase());
}
assert_eq!(map["lorem"], "LOREM");
assert_eq!(map["ipsum"], "IPSUM");

use indexmap::IndexMap;

let mut map = IndexMap::new();
map.insert("foo", 1);
println!("{:?}", map["bar"]); // panics!

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

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

Panics if key is not present in the map.

type Output = V

The returned type after indexing.

impl<K, V, S> Index<usize> for IndexMap<K, V, S>

Access IndexMap values at indexed positions.

Examples

use indexmap::IndexMap;

let mut map = IndexMap::new();
for word in "Lorem ipsum dolor sit amet".split_whitespace() {
    map.insert(word.to_lowercase(), word.to_uppercase());
}
assert_eq!(map[0], "LOREM");
assert_eq!(map[1], "IPSUM");
map.reverse();
assert_eq!(map[0], "AMET");
assert_eq!(map[1], "SIT");
map.sort_keys();
assert_eq!(map[0], "AMET");
assert_eq!(map[1], "DOLOR");

use indexmap::IndexMap;

let mut map = IndexMap::new();
map.insert("foo", 1);
println!("{:?}", map[10]); // panics!

fn index(&self, index: usize) -> &V

Returns a reference to the value at the supplied index.

Panics if index is out of bounds.

type Output = V

The returned type after indexing.

impl<K, V, Q, S> IndexMut<&Q> for IndexMap<K, V, S>

where Q: Hash + Equivalent<K> + ?Sized, K: Hash + Eq, S: BuildHasher,

Access IndexMap values corresponding to a key.

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().

Examples

use indexmap::IndexMap;

let mut map = IndexMap::new();
for word in "Lorem ipsum dolor sit amet".split_whitespace() {
    map.insert(word.to_lowercase(), word.to_string());
}
let lorem = &mut map["lorem"];
assert_eq!(lorem, "Lorem");
lorem.retain(char::is_lowercase);
assert_eq!(map["lorem"], "orem");

use indexmap::IndexMap;

let mut map = IndexMap::new();
map.insert("foo", 1);
map["bar"] = 1; // panics!

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

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

Panics if key is not present in the map.

impl<K, V, S> IndexMut<usize> for IndexMap<K, V, S>

Access IndexMap values at indexed positions.

Mutable indexing allows changing / updating indexed values that are already present.

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

Examples

use indexmap::IndexMap;

let mut map = IndexMap::new();
for word in "Lorem ipsum dolor sit amet".split_whitespace() {
    map.insert(word.to_lowercase(), word.to_string());
}
let lorem = &mut map[0];
assert_eq!(lorem, "Lorem");
lorem.retain(char::is_lowercase);
assert_eq!(map["lorem"], "orem");

use indexmap::IndexMap;

let mut map = IndexMap::new();
map.insert("foo", 1);
map[10] = 1; // panics!

fn index_mut(&mut self, index: usize) -> &mut V

Returns a mutable reference to the value at the supplied index.

Panics if index is out of bounds.

impl<'a, K, V, S> IntoIterator for &'a IndexMap<K, V, S>

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>

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>

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<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>(&mut self, key: &Q) -> Option<(usize, &mut K, &mut V)>

where Q: Hash + Equivalent<K> + ?Sized,

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, 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

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

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

where K: Eq + Hash, V: Eq, S: BuildHasher,