Struct IndexSet

pub struct IndexSet<T, S = RandomState> { /* private fields */ }

A hash set where the iteration order of the values is independent of their hash values.

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

Order

The values have a consistent order that is determined by the sequence of insertion and removal calls on the set. The order does not depend on the values or the hash function at all. Note that insertion order and value are not affected if a re-insertion is attempted once an element is already present.

All iterators traverse the set in order. Set operation iterators like union produce a concatenated order, as do their matching “bitwise” operators. See their documentation for specifics.

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 values 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 value, and the method .get_index looks up the value by index.

Examples

use indexmap::IndexSet;

// Collects which letters appear in a sentence.
let letters: IndexSet<_> = "a short treatise on fungi".chars().collect();

assert!(letters.contains(&'s'));
assert!(letters.contains(&'t'));
assert!(letters.contains(&'u'));
assert!(!letters.contains(&'y'));

Implementations

impl<T> IndexSet<T>

pub fn new() -> Self

Create a new set. (Does not allocate.)

pub fn with_capacity(n: usize) -> Self

Create a new set with capacity for n elements. (Does not allocate if n is zero.)

Computes in O(n) time.

impl<T, S> IndexSet<T, S>

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

Create a new set with capacity for n elements. (Does not allocate if n is zero.)

Computes in O(n) time.

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

Create a new set 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 set’s BuildHasher.

pub fn len(&self) -> usize

Return the number of elements in the set.

Computes in O(1) time.

pub fn is_empty(&self) -> bool

Returns true if the set contains no elements.

Computes in O(1) time.

pub fn iter(&self) -> Iter<'_, T>

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

pub fn clear(&mut self)

Remove all elements in the set, while preserving its capacity.

Computes in O(n) time.

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

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

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

pub fn drain<R>(&mut self, range: R) -> Drain<'_, T>

where R: RangeBounds<usize>,

Clears the IndexSet in the given index range, returning those values 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 set entirely, use RangeFull like set.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 set.

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 set containing the elements in the range [at, len). After the call, the original set will be left containing the elements [0, at) with its previous capacity unchanged.

Panics if at > len.

impl<T, S> IndexSet<T, S>

where T: Hash + Eq, S: BuildHasher,

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

Reserve capacity for additional more values.

Computes in O(n) time.

pub fn shrink_to_fit(&mut self)

Shrink the capacity of the set as much as possible.

Computes in O(n) time.

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

Shrink the capacity of the set with a lower limit.

Computes in O(n) time.

pub fn insert(&mut self, value: T) -> bool

Insert the value into the set.

If an equivalent item already exists in the set, it returns false leaving the original value in the set and without altering its insertion order. Otherwise, it inserts the new item and returns true.

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

pub fn insert_full(&mut self, value: T) -> (usize, bool)

Insert the value into the set, and get its index.

If an equivalent item already exists in the set, it returns the index of the existing item and false, leaving the original value in the set and without altering its insertion order. Otherwise, it inserts the new item and returns the index of the inserted item and true.

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

pub fn difference<'a, S2>( &'a self, other: &'a IndexSet<T, S2>, ) -> Difference<'a, T, S2>

where S2: BuildHasher,

Return an iterator over the values that are in self but not other.

Values are produced in the same order that they appear in self.

pub fn symmetric_difference<'a, S2>( &'a self, other: &'a IndexSet<T, S2>, ) -> SymmetricDifference<'a, T, S, S2>

where S2: BuildHasher,

Return an iterator over the values that are in self or other, but not in both.

Values from self are produced in their original order, followed by values from other in their original order.

pub fn intersection<'a, S2>( &'a self, other: &'a IndexSet<T, S2>, ) -> Intersection<'a, T, S2>

where S2: BuildHasher,

Return an iterator over the values that are in both self and other.

Values are produced in the same order that they appear in self.

pub fn union<'a, S2>(&'a self, other: &'a IndexSet<T, S2>) -> Union<'a, T, S>

where S2: BuildHasher,

Return an iterator over all values that are in self or other.

Values from self are produced in their original order, followed by values that are unique to other in their original order.

pub fn contains<Q>(&self, value: &Q) -> bool

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

Return true if an equivalent to value exists in the set.

Computes in O(1) time (average).

pub fn get<Q>(&self, value: &Q) -> Option<&T>

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

Return a reference to the value stored in the set, if it is present, else None.

Computes in O(1) time (average).

pub fn get_full<Q>(&self, value: &Q) -> Option<(usize, &T)>

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

Return item index and value

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

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

Return item index, if it exists in the set

pub fn replace(&mut self, value: T) -> Option<T>

Adds a value to the set, replacing the existing value, if any, that is equal to the given one, without altering its insertion order. Returns the replaced value.

Computes in O(1) time (average).

pub fn replace_full(&mut self, value: T) -> (usize, Option<T>)

Adds a value to the set, replacing the existing value, if any, that is equal to the given one, without altering its insertion order. Returns the index of the item and its replaced value.

Computes in O(1) time (average).

pub fn remove<Q>(&mut self, value: &Q) -> bool

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

Remove the value from the set, and return true if it was present.

NOTE: This is equivalent to .swap_remove(value), if you want to preserve the order of the values in the set, use .shift_remove(value).

Computes in O(1) time (average).

pub fn swap_remove<Q>(&mut self, value: &Q) -> bool

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

Remove the value from the set, and return true if it was present.

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

Return false if value was not in the set.

Computes in O(1) time (average).

pub fn shift_remove<Q>(&mut self, value: &Q) -> bool

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

Remove the value from the set, and return true if it was present.

Like Vec::remove, the value 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 false if value was not in the set.

Computes in O(n) time (average).

pub fn take<Q>(&mut self, value: &Q) -> Option<T>

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

Removes and returns the value in the set, if any, that is equal to the given one.

NOTE: This is equivalent to .swap_take(value), if you need to preserve the order of the values in the set, use .shift_take(value) instead.

Computes in O(1) time (average).

pub fn swap_take<Q>(&mut self, value: &Q) -> Option<T>

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

Removes and returns the value in the set, if any, that is equal to the given one.

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

Return None if value was not in the set.

Computes in O(1) time (average).

pub fn shift_take<Q>(&mut self, value: &Q) -> Option<T>

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

Removes and returns the value in the set, if any, that is equal to the given one.

Like Vec::remove, the value 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 value was not in the set.

Computes in O(n) time (average).

pub fn swap_remove_full<Q>(&mut self, value: &Q) -> Option<(usize, T)>

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

Remove the value from the set return it and the index it had.

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

Return None if value was not in the set.

pub fn shift_remove_full<Q>(&mut self, value: &Q) -> Option<(usize, T)>

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

Remove the value from the set return it and the index it had.

Like Vec::remove, the value 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 value was not in the set.

pub fn pop(&mut self) -> Option<T>

Remove the last value

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(&T) -> bool,

Scan through each value in the set 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(&mut self)

where T: Ord,

Sort the set’s values by their default ordering.

See sort_by for details.

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

where F: FnMut(&T, &T) -> Ordering,

Sort the set’s values in place using the comparison function cmp.

Computes in O(n log n) time and O(n) space. The sort is stable.

pub fn sorted_by<F>(self, cmp: F) -> IntoIter<T>

where F: FnMut(&T, &T) -> Ordering,

Sort the values of the set and return a by-value iterator of the values with the result.

The sort is stable.

pub fn sort_unstable(&mut self)

where T: Ord,

Sort the set’s values by their default ordering.

See sort_unstable_by for details.

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

where F: FnMut(&T, &T) -> Ordering,

Sort the set’s values in place using the comparison funtion cmp.

Computes in O(n log n) time. The sort is unstable.

pub fn sorted_unstable_by<F>(self, cmp: F) -> IntoIter<T>

where F: FnMut(&T, &T) -> Ordering,

Sort the values of the set and return a by-value iterator of the values with the result.

pub fn reverse(&mut self)

Reverses the order of the set’s values in place.

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

impl<T, S> IndexSet<T, S>

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

Get a value by index

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

Computes in O(1) time.

pub fn first(&self) -> Option<&T>

Get the first value

Computes in O(1) time.

pub fn last(&self) -> Option<&T>

Get the last value

Computes in O(1) time.

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

Remove the value by index

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

Like Vec::swap_remove, the value is removed by swapping it with the last element of the set 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<T>

Remove the value by index

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

Like Vec::remove, the value 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 value from one index to another by shifting all other values in-between.

• If from < to, the other values will shift down while the targeted value moves up.
• If from > to, the other values will shift up while the targeted value 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 values in the set.

Panics if a or b are out of bounds.

impl<T, S> IndexSet<T, S>

where T: Eq + Hash, S: BuildHasher,

pub fn is_disjoint<S2>(&self, other: &IndexSet<T, S2>) -> bool

where S2: BuildHasher,

Returns true if self has no elements in common with other.

pub fn is_subset<S2>(&self, other: &IndexSet<T, S2>) -> bool

where S2: BuildHasher,

Returns true if all elements of self are contained in other.

pub fn is_superset<S2>(&self, other: &IndexSet<T, S2>) -> bool

where S2: BuildHasher,

Returns true if all elements of other are contained in self.

Trait Implementations

impl<T, S1, S2> BitAnd<&IndexSet<T, S2>> for &IndexSet<T, S1>

where T: Eq + Hash + Clone, S1: BuildHasher + Default, S2: BuildHasher,

fn bitand(self, other: &IndexSet<T, S2>) -> Self::Output

Returns the set intersection, cloned into a new set.

Values are collected in the same order that they appear in self.

type Output = IndexSet<T, S1>

The resulting type after applying the & operator.

impl<T, S1, S2> BitOr<&IndexSet<T, S2>> for &IndexSet<T, S1>

where T: Eq + Hash + Clone, S1: BuildHasher + Default, S2: BuildHasher,

fn bitor(self, other: &IndexSet<T, S2>) -> Self::Output

Returns the set union, cloned into a new set.

Values from self are collected in their original order, followed by values that are unique to other in their original order.

type Output = IndexSet<T, S1>

The resulting type after applying the | operator.

impl<T, S1, S2> BitXor<&IndexSet<T, S2>> for &IndexSet<T, S1>

where T: Eq + Hash + Clone, S1: BuildHasher + Default, S2: BuildHasher,

fn bitxor(self, other: &IndexSet<T, S2>) -> Self::Output

Returns the set symmetric-difference, cloned into a new set.

Values from self are collected in their original order, followed by values from other in their original order.

type Output = IndexSet<T, S1>

The resulting type after applying the ^ operator.

impl<T, S> Clone for IndexSet<T, S>

where T: 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<T, S> Debug for IndexSet<T, S>

where T: Debug,

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

Formats the value using the given formatter.

impl<T, S> Default for IndexSet<T, S>

where S: Default,

fn default() -> Self

Return an empty IndexSet

impl<'a, T, S> Extend<&'a T> for IndexSet<T, S>

where T: Hash + Eq + Copy + 'a, S: BuildHasher,

fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iterable: I)

Extends a collection with the contents of an iterator.

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<T, S> Extend<T> for IndexSet<T, S>

where T: Hash + Eq, S: BuildHasher,

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

Extends a collection with the contents of an iterator.

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<T, const N: usize> From<[T; N]> for IndexSet<T, RandomState>

where T: Eq + Hash,

fn from(arr: [T; N]) -> Self

Examples

use indexmap::IndexSet;

let set1 = IndexSet::from([1, 2, 3, 4]);
let set2: IndexSet<_> = [1, 2, 3, 4].into();
assert_eq!(set1, set2);

impl<T, S> FromIterator<T> for IndexSet<T, S>

where T: Hash + Eq, S: BuildHasher + Default,

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

Creates a value from an iterator.

impl<T, S> Index<usize> for IndexSet<T, S>

Access IndexSet values at indexed positions.

Examples

use indexmap::IndexSet;

let mut set = IndexSet::new();
for word in "Lorem ipsum dolor sit amet".split_whitespace() {
    set.insert(word.to_string());
}
assert_eq!(set[0], "Lorem");
assert_eq!(set[1], "ipsum");
set.reverse();
assert_eq!(set[0], "amet");
assert_eq!(set[1], "sit");
set.sort();
assert_eq!(set[0], "Lorem");
assert_eq!(set[1], "amet");

use indexmap::IndexSet;

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

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

Returns a reference to the value at the supplied index.

Panics if index is out of bounds.

type Output = T

The returned type after indexing.

impl<'a, T, S> IntoIterator for &'a IndexSet<T, S>

type Item = &'a T

The type of the elements being iterated over.

type IntoIter = Iter<'a, T>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<T, S> IntoIterator for IndexSet<T, S>

type Item = T

The type of the elements being iterated over.

type IntoIter = IntoIter<T>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<T, S1, S2> PartialEq<IndexSet<T, S2>> for IndexSet<T, S1>

where T: Hash + Eq, S1: BuildHasher, S2: BuildHasher,

fn eq(&self, other: &IndexSet<T, 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<T, S1, S2> Sub<&IndexSet<T, S2>> for &IndexSet<T, S1>

where T: Eq + Hash + Clone, S1: BuildHasher + Default, S2: BuildHasher,

fn sub(self, other: &IndexSet<T, S2>) -> Self::Output

Returns the set difference, cloned into a new set.

Values are collected in the same order that they appear in self.

type Output = IndexSet<T, S1>

The resulting type after applying the - operator.

impl<T, S> Eq for IndexSet<T, S>

where T: Eq + Hash, S: BuildHasher,