pub struct IndexMap<K, V, S = RandomState> {
    core: IndexMapCore<K, V>,
    hash_builder: S,
}
Expand description

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);

Fields

core: IndexMapCore<K, V>hash_builder: S

Implementations

Create a new map. (Does not allocate.)

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

Computes in O(n) time.

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

Computes in O(n) time.

Create a new map with hash_builder

Computes in O(1) time.

Return a reference to the map’s BuildHasher.

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

Computes in O(1) time.

Returns true if the map contains no elements.

Computes in O(1) time.

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

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

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

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

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

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

Computes in O(n) time.

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.

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.

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.

Reserve capacity for additional more key-value pairs.

Computes in O(n) time.

Shrink the capacity of the map as much as possible.

Computes in O(n) time.

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.

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.

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

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

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

Computes in O(1) time (average).

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

Computes in O(1) time (average).

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

Computes in O(1) time (average).

Return item index, key and value

Return item index, if it exists in the map

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).

source

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

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).

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).

source

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

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 postion of what used to be the last element!

Return None if key is not in map.

Computes in O(1) time (average).

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).

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).

source

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

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).

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).

Remove the last key-value pair

Computes in O(1) time (average).

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).

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

See sort_by for details.

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.

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.

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

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

Get a key-value pair by index

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

Computes in O(1) time.

Get a key-value pair by index

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

Computes in O(1) time.

Get the first key-value pair

Computes in O(1) time.

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

Computes in O(1) time.

Get the last key-value pair

Computes in O(1) time.

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

Computes in O(1) time.

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).

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).

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

Panics if a or b are out of bounds.

Trait Implementations

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

Formats the value using the given formatter. Read more

Return an empty IndexMap

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

See the first extend method for more details.

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

Extends a collection with exactly one element.

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

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

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.

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

Extends a collection with exactly one element.

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

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

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.

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!

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

Panics if key is not present in the map.

The returned type after indexing.

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!

Returns a reference to the value at the supplied index.

Panics if index is out of bounds.

The returned type after indexing.

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!

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

Panics if key is not present in the map.

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!

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

Panics if index is out of bounds.

The type of the elements being iterated over.

Which kind of iterator are we turning this into?

Creates an iterator from a value. Read more

The type of the elements being iterated over.

Which kind of iterator are we turning this into?

Creates an iterator from a value. Read more

The type of the elements being iterated over.

Which kind of iterator are we turning this into?

Creates an iterator from a value. Read more

Opt-in mutable access to keys.

See MutableKeys for more information.

Return item index, mutable reference to key and value

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

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. Read more

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

This method tests for !=.

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

The resulting type after obtaining ownership.

Creates owned data from borrowed data, usually by cloning. Read more

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

Uses borrowed data to replace owned data, usually by cloning. Read more

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.