Struct std::collections::BTreeSet

pub struct BTreeSet<T, A = Global>where
    A: Allocator + Clone,{ /* private fields */ }

An ordered set based on a B-Tree.

See BTreeMap’s documentation for a detailed discussion of this collection’s performance benefits and drawbacks.

It is a logic error for an item to be modified in such a way that the item’s ordering relative to any other item, as determined by the Ord trait, changes while it is in the set. This is normally only possible through Cell, RefCell, global state, I/O, or unsafe code. The behavior resulting from such a logic error is not specified, but will be encapsulated to the BTreeSet that observed the logic error and not result in undefined behavior. This could include panics, incorrect results, aborts, memory leaks, and non-termination.

Iterators returned by BTreeSet::iter produce their items in order, and take worst-case logarithmic and amortized constant time per item returned.

Examples

use std::collections::BTreeSet;

// Type inference lets us omit an explicit type signature (which
// would be `BTreeSet<&str>` in this example).
let mut books = BTreeSet::new();

// Add some books.
books.insert("A Dance With Dragons");
books.insert("To Kill a Mockingbird");
books.insert("The Odyssey");
books.insert("The Great Gatsby");

// Check for a specific one.
if !books.contains("The Winds of Winter") {
    println!("We have {} books, but The Winds of Winter ain't one.",
             books.len());
}

// Remove a book.
books.remove("The Odyssey");

// Iterate over everything.
for book in &books {
    println!("{book}");
}

A BTreeSet with a known list of items can be initialized from an array:

use std::collections::BTreeSet;

let set = BTreeSet::from([1, 2, 3]);

Implementations

impl<T> BTreeSet<T, Global>

pub const fn new() -> BTreeSet<T, Global>

Makes a new, empty BTreeSet.

Does not allocate anything on its own.

Examples

use std::collections::BTreeSet;

let mut set: BTreeSet<i32> = BTreeSet::new();

impl<T, A> BTreeSet<T, A>where
    A: Allocator + Clone,

pub fn new_in(alloc: A) -> BTreeSet<T, A>

🔬This is a nightly-only experimental API. (btreemap_alloc #32838)

Makes a new BTreeSet with a reasonable choice of B.

Examples

use std::collections::BTreeSet;
use std::alloc::Global;

let mut set: BTreeSet<i32> = BTreeSet::new_in(Global);

pub fn range<K, R>(&self, range: R) -> Range<'_, T>where
    K: Ord + ?Sized,
    T: Borrow<K> + Ord,
    R: RangeBounds<K>,

Constructs a double-ended iterator over a sub-range of elements in the set. The simplest way is to use the range syntax min..max, thus range(min..max) will yield elements from min (inclusive) to max (exclusive). The range may also be entered as (Bound<T>, Bound<T>), so for example range((Excluded(4), Included(10))) will yield a left-exclusive, right-inclusive range from 4 to 10.

Panics

Panics if range start > end. Panics if range start == end and both bounds are Excluded.

Examples

use std::collections::BTreeSet;
use std::ops::Bound::Included;

let mut set = BTreeSet::new();
set.insert(3);
set.insert(5);
set.insert(8);
for &elem in set.range((Included(&4), Included(&8))) {
    println!("{elem}");
}
assert_eq!(Some(&5), set.range(4..).next());

pub fn difference(&'a self, other: &'a BTreeSet<T, A>) -> Difference<'a, T, A>where
    T: Ord,

Visits the elements representing the difference, i.e., the elements that are in self but not in other, in ascending order.

Examples

use std::collections::BTreeSet;

let mut a = BTreeSet::new();
a.insert(1);
a.insert(2);

let mut b = BTreeSet::new();
b.insert(2);
b.insert(3);

let diff: Vec<_> = a.difference(&b).cloned().collect();
assert_eq!(diff, [1]);

pub fn symmetric_difference(
    &'a self,
    other: &'a BTreeSet<T, A>
) -> SymmetricDifference<'a, T>where
    T: Ord,

Visits the elements representing the symmetric difference, i.e., the elements that are in self or in other but not in both, in ascending order.

Examples

use std::collections::BTreeSet;

let mut a = BTreeSet::new();
a.insert(1);
a.insert(2);

let mut b = BTreeSet::new();
b.insert(2);
b.insert(3);

let sym_diff: Vec<_> = a.symmetric_difference(&b).cloned().collect();
assert_eq!(sym_diff, [1, 3]);

pub fn intersection(
    &'a self,
    other: &'a BTreeSet<T, A>
) -> Intersection<'a, T, A>where
    T: Ord,

Visits the elements representing the intersection, i.e., the elements that are both in self and other, in ascending order.

Examples

use std::collections::BTreeSet;

let mut a = BTreeSet::new();
a.insert(1);
a.insert(2);

let mut b = BTreeSet::new();
b.insert(2);
b.insert(3);

let intersection: Vec<_> = a.intersection(&b).cloned().collect();
assert_eq!(intersection, [2]);

pub fn union(&'a self, other: &'a BTreeSet<T, A>) -> Union<'a, T>where
    T: Ord,

Visits the elements representing the union, i.e., all the elements in self or other, without duplicates, in ascending order.

Examples

use std::collections::BTreeSet;

let mut a = BTreeSet::new();
a.insert(1);

let mut b = BTreeSet::new();
b.insert(2);

let union: Vec<_> = a.union(&b).cloned().collect();
assert_eq!(union, [1, 2]);

pub fn clear(&mut self)where
    A: Clone,

Clears the set, removing all elements.

Examples

use std::collections::BTreeSet;

let mut v = BTreeSet::new();
v.insert(1);
v.clear();
assert!(v.is_empty());

pub fn contains<Q>(&self, value: &Q) -> boolwhere
    T: Borrow<Q> + Ord,
    Q: Ord + ?Sized,

Returns true if the set contains an element equal to the value.

The value may be any borrowed form of the set’s element type, but the ordering on the borrowed form must match the ordering on the element type.

Examples

use std::collections::BTreeSet;

let set = BTreeSet::from([1, 2, 3]);
assert_eq!(set.contains(&1), true);
assert_eq!(set.contains(&4), false);

pub fn get<Q>(&self, value: &Q) -> Option<&T>where
    T: Borrow<Q> + Ord,
    Q: Ord + ?Sized,

Returns a reference to the element in the set, if any, that is equal to the value.

The value may be any borrowed form of the set’s element type, but the ordering on the borrowed form must match the ordering on the element type.

Examples

use std::collections::BTreeSet;

let set = BTreeSet::from([1, 2, 3]);
assert_eq!(set.get(&2), Some(&2));
assert_eq!(set.get(&4), None);

pub fn is_disjoint(&self, other: &BTreeSet<T, A>) -> boolwhere
    T: Ord,

Returns true if self has no elements in common with other. This is equivalent to checking for an empty intersection.

Examples

use std::collections::BTreeSet;

let a = BTreeSet::from([1, 2, 3]);
let mut b = BTreeSet::new();

assert_eq!(a.is_disjoint(&b), true);
b.insert(4);
assert_eq!(a.is_disjoint(&b), true);
b.insert(1);
assert_eq!(a.is_disjoint(&b), false);

pub fn is_subset(&self, other: &BTreeSet<T, A>) -> boolwhere
    T: Ord,

Returns true if the set is a subset of another, i.e., other contains at least all the elements in self.

Examples

use std::collections::BTreeSet;

let sup = BTreeSet::from([1, 2, 3]);
let mut set = BTreeSet::new();

assert_eq!(set.is_subset(&sup), true);
set.insert(2);
assert_eq!(set.is_subset(&sup), true);
set.insert(4);
assert_eq!(set.is_subset(&sup), false);

pub fn is_superset(&self, other: &BTreeSet<T, A>) -> boolwhere
    T: Ord,

Returns true if the set is a superset of another, i.e., self contains at least all the elements in other.

Examples

use std::collections::BTreeSet;

let sub = BTreeSet::from([1, 2]);
let mut set = BTreeSet::new();

assert_eq!(set.is_superset(&sub), false);

set.insert(0);
set.insert(1);
assert_eq!(set.is_superset(&sub), false);

set.insert(2);
assert_eq!(set.is_superset(&sub), true);

pub fn first(&self) -> Option<&T>where
    T: Ord,

🔬This is a nightly-only experimental API. (map_first_last #62924)

Returns a reference to the first element in the set, if any. This element is always the minimum of all elements in the set.

Examples

Basic usage:

#![feature(map_first_last)]
use std::collections::BTreeSet;

let mut set = BTreeSet::new();
assert_eq!(set.first(), None);
set.insert(1);
assert_eq!(set.first(), Some(&1));
set.insert(2);
assert_eq!(set.first(), Some(&1));

pub fn last(&self) -> Option<&T>where
    T: Ord,

🔬This is a nightly-only experimental API. (map_first_last #62924)

Returns a reference to the last element in the set, if any. This element is always the maximum of all elements in the set.

Examples

Basic usage:

#![feature(map_first_last)]
use std::collections::BTreeSet;

let mut set = BTreeSet::new();
assert_eq!(set.last(), None);
set.insert(1);
assert_eq!(set.last(), Some(&1));
set.insert(2);
assert_eq!(set.last(), Some(&2));

pub fn pop_first(&mut self) -> Option<T>where
    T: Ord,

🔬This is a nightly-only experimental API. (map_first_last #62924)

Removes the first element from the set and returns it, if any. The first element is always the minimum element in the set.

Examples

#![feature(map_first_last)]
use std::collections::BTreeSet;

let mut set = BTreeSet::new();

set.insert(1);
while let Some(n) = set.pop_first() {
    assert_eq!(n, 1);
}
assert!(set.is_empty());

pub fn pop_last(&mut self) -> Option<T>where
    T: Ord,

🔬This is a nightly-only experimental API. (map_first_last #62924)

Removes the last element from the set and returns it, if any. The last element is always the maximum element in the set.

Examples

#![feature(map_first_last)]
use std::collections::BTreeSet;

let mut set = BTreeSet::new();

set.insert(1);
while let Some(n) = set.pop_last() {
    assert_eq!(n, 1);
}
assert!(set.is_empty());

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

Adds a value to the set.

Returns whether the value was newly inserted. That is:

• If the set did not previously contain an equal value, true is returned.
• If the set already contained an equal value, false is returned, and the entry is not updated.

See the module-level documentation for more.

Examples

use std::collections::BTreeSet;

let mut set = BTreeSet::new();

assert_eq!(set.insert(2), true);
assert_eq!(set.insert(2), false);
assert_eq!(set.len(), 1);

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

Adds a value to the set, replacing the existing element, if any, that is equal to the value. Returns the replaced element.

Examples

use std::collections::BTreeSet;

let mut set = BTreeSet::new();
set.insert(Vec::<i32>::new());

assert_eq!(set.get(&[][..]).unwrap().capacity(), 0);
set.replace(Vec::with_capacity(10));
assert_eq!(set.get(&[][..]).unwrap().capacity(), 10);

pub fn remove<Q>(&mut self, value: &Q) -> boolwhere
    T: Borrow<Q> + Ord,
    Q: Ord + ?Sized,

If the set contains an element equal to the value, removes it from the set and drops it. Returns whether such an element was present.

The value may be any borrowed form of the set’s element type, but the ordering on the borrowed form must match the ordering on the element type.

Examples

use std::collections::BTreeSet;

let mut set = BTreeSet::new();

set.insert(2);
assert_eq!(set.remove(&2), true);
assert_eq!(set.remove(&2), false);

pub fn take<Q>(&mut self, value: &Q) -> Option<T>where
    T: Borrow<Q> + Ord,
    Q: Ord + ?Sized,

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

The value may be any borrowed form of the set’s element type, but the ordering on the borrowed form must match the ordering on the element type.

Examples

use std::collections::BTreeSet;

let mut set = BTreeSet::from([1, 2, 3]);
assert_eq!(set.take(&2), Some(2));
assert_eq!(set.take(&2), None);

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

Retains only the elements specified by the predicate.

In other words, remove all elements e for which f(&e) returns false. The elements are visited in ascending order.

Examples

use std::collections::BTreeSet;

let mut set = BTreeSet::from([1, 2, 3, 4, 5, 6]);
// Keep only the even numbers.
set.retain(|&k| k % 2 == 0);
assert!(set.iter().eq([2, 4, 6].iter()));

pub fn append(&mut self, other: &mut BTreeSet<T, A>)where
    T: Ord,
    A: Clone,

Moves all elements from other into self, leaving other empty.

Examples

use std::collections::BTreeSet;

let mut a = BTreeSet::new();
a.insert(1);
a.insert(2);
a.insert(3);

let mut b = BTreeSet::new();
b.insert(3);
b.insert(4);
b.insert(5);

a.append(&mut b);

assert_eq!(a.len(), 5);
assert_eq!(b.len(), 0);

assert!(a.contains(&1));
assert!(a.contains(&2));
assert!(a.contains(&3));
assert!(a.contains(&4));
assert!(a.contains(&5));

pub fn split_off<Q>(&mut self, value: &Q) -> BTreeSet<T, A>where
    Q: Ord + ?Sized,
    T: Borrow<Q> + Ord,
    A: Clone,

Splits the collection into two at the value. Returns a new collection with all elements greater than or equal to the value.

Examples

Basic usage:

use std::collections::BTreeSet;

let mut a = BTreeSet::new();
a.insert(1);
a.insert(2);
a.insert(3);
a.insert(17);
a.insert(41);

let b = a.split_off(&3);

assert_eq!(a.len(), 2);
assert_eq!(b.len(), 3);

assert!(a.contains(&1));
assert!(a.contains(&2));

assert!(b.contains(&3));
assert!(b.contains(&17));
assert!(b.contains(&41));

pub fn drain_filter<'a, F>(&'a mut self, pred: F) -> DrainFilter<'a, T, F, A>where
    T: Ord,
    F: 'a + FnMut(&T) -> bool,

🔬This is a nightly-only experimental API. (btree_drain_filter #70530)

Creates an iterator that visits all elements in ascending order and uses a closure to determine if an element should be removed.

If the closure returns true, the element is removed from the set and yielded. If the closure returns false, or panics, the element remains in the set and will not be yielded.

If the iterator is only partially consumed or not consumed at all, each of the remaining elements is still subjected to the closure and removed and dropped if it returns true.

It is unspecified how many more elements will be subjected to the closure if a panic occurs in the closure, or if a panic occurs while dropping an element, or if the DrainFilter itself is leaked.

Examples

Splitting a set into even and odd values, reusing the original set:

#![feature(btree_drain_filter)]
use std::collections::BTreeSet;

let mut set: BTreeSet<i32> = (0..8).collect();
let evens: BTreeSet<_> = set.drain_filter(|v| v % 2 == 0).collect();
let odds = set;
assert_eq!(evens.into_iter().collect::<Vec<_>>(), vec![0, 2, 4, 6]);
assert_eq!(odds.into_iter().collect::<Vec<_>>(), vec![1, 3, 5, 7]);

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

Gets an iterator that visits the elements in the BTreeSet in ascending order.

Examples

use std::collections::BTreeSet;

let set = BTreeSet::from([1, 2, 3]);
let mut set_iter = set.iter();
assert_eq!(set_iter.next(), Some(&1));
assert_eq!(set_iter.next(), Some(&2));
assert_eq!(set_iter.next(), Some(&3));
assert_eq!(set_iter.next(), None);

Values returned by the iterator are returned in ascending order:

use std::collections::BTreeSet;

let set = BTreeSet::from([3, 1, 2]);
let mut set_iter = set.iter();
assert_eq!(set_iter.next(), Some(&1));
assert_eq!(set_iter.next(), Some(&2));
assert_eq!(set_iter.next(), Some(&3));
assert_eq!(set_iter.next(), None);

pub fn len(&self) -> usize

Returns the number of elements in the set.

Examples

use std::collections::BTreeSet;

let mut v = BTreeSet::new();
assert_eq!(v.len(), 0);
v.insert(1);
assert_eq!(v.len(), 1);

pub fn is_empty(&self) -> bool

Returns true if the set contains no elements.

Examples

use std::collections::BTreeSet;

let mut v = BTreeSet::new();
assert!(v.is_empty());
v.insert(1);
assert!(!v.is_empty());

Trait Implementations

impl<T, A> BitAnd<&BTreeSet<T, A>> for &BTreeSet<T, A>where
    T: Ord + Clone,
    A: Allocator + Clone,

fn bitand(self, rhs: &BTreeSet<T, A>) -> BTreeSet<T, A>

Returns the intersection of self and rhs as a new BTreeSet<T>.

Examples

use std::collections::BTreeSet;

let a = BTreeSet::from([1, 2, 3]);
let b = BTreeSet::from([2, 3, 4]);

let result = &a & &b;
assert_eq!(result, BTreeSet::from([2, 3]));

type Output = BTreeSet<T, A>

The resulting type after applying the & operator.

impl<T, A> BitOr<&BTreeSet<T, A>> for &BTreeSet<T, A>where
    T: Ord + Clone,
    A: Allocator + Clone,

fn bitor(self, rhs: &BTreeSet<T, A>) -> BTreeSet<T, A>

Returns the union of self and rhs as a new BTreeSet<T>.

Examples

use std::collections::BTreeSet;

let a = BTreeSet::from([1, 2, 3]);
let b = BTreeSet::from([3, 4, 5]);

let result = &a | &b;
assert_eq!(result, BTreeSet::from([1, 2, 3, 4, 5]));

type Output = BTreeSet<T, A>

The resulting type after applying the | operator.

impl<T, A> BitXor<&BTreeSet<T, A>> for &BTreeSet<T, A>where
    T: Ord + Clone,
    A: Allocator + Clone,

fn bitxor(self, rhs: &BTreeSet<T, A>) -> BTreeSet<T, A>

Returns the symmetric difference of self and rhs as a new BTreeSet<T>.

Examples

use std::collections::BTreeSet;

let a = BTreeSet::from([1, 2, 3]);
let b = BTreeSet::from([2, 3, 4]);

let result = &a ^ &b;
assert_eq!(result, BTreeSet::from([1, 4]));

type Output = BTreeSet<T, A>

The resulting type after applying the ^ operator.

impl<T, A> Clone for BTreeSet<T, A>where
    T: Clone,
    A: Allocator + Clone,

fn clone(&self) -> BTreeSet<T, A>

Returns a copy of the value.

fn clone_from(&mut self, other: &BTreeSet<T, A>)

Performs copy-assignment from source.

impl<T, A> Debug for BTreeSet<T, A>where
    T: Debug,
    A: Allocator + Clone,

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

Formats the value using the given formatter.

impl<T> Default for BTreeSet<T, Global>

fn default() -> BTreeSet<T, Global>

Creates an empty BTreeSet.

impl<'a, T, A> Extend<&'a T> for BTreeSet<T, A>where
    T: 'a + Ord + Copy,
    A: Allocator + Clone,

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

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, &'a T)

🔬This is a nightly-only experimental API. (extend_one #72631)

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (extend_one #72631)

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

impl<T, A> Extend<T> for BTreeSet<T, A>where
    T: Ord,
    A: Allocator + Clone,

fn extend<Iter>(&mut self, iter: Iter)where
    Iter: IntoIterator<Item = T>,

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, elem: T)

🔬This is a nightly-only experimental API. (extend_one #72631)

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (extend_one #72631)

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

impl<T, const N: usize> From<[T; N]> for BTreeSet<T, Global>where
    T: Ord,

fn from(arr: [T; N]) -> BTreeSet<T, Global>

Converts a [T; N] into a BTreeSet<T>.

use std::collections::BTreeSet;

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

impl<T> FromIterator<T> for BTreeSet<T, Global>where
    T: Ord,

fn from_iter<I>(iter: I) -> BTreeSet<T, Global>where
    I: IntoIterator<Item = T>,

Creates a value from an iterator.

impl<T, A> Hash for BTreeSet<T, A>where
    T: Hash,
    A: Allocator + Clone,

fn hash<H>(&self, state: &mut H)where
    H: Hasher,

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)where
    H: Hasher,

Feeds a slice of this type into the given Hasher.

impl<'a, T, A> IntoIterator for &'a BTreeSet<T, A>where
    A: Allocator + Clone,

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) -> Iter<'a, T>

Creates an iterator from a value.

impl<T, A> IntoIterator for BTreeSet<T, A>where
    A: Allocator + Clone,

fn into_iter(self) -> IntoIter<T, A>

Gets an iterator for moving out the BTreeSet’s contents.

Examples

use std::collections::BTreeSet;

let set = BTreeSet::from([1, 2, 3, 4]);

let v: Vec<_> = set.into_iter().collect();
assert_eq!(v, [1, 2, 3, 4]);

type Item = T

The type of the elements being iterated over.

type IntoIter = IntoIter<T, A>

Which kind of iterator are we turning this into?

impl<T, A> Ord for BTreeSet<T, A>where
    T: Ord,
    A: Allocator + Clone,

fn cmp(&self, other: &BTreeSet<T, A>) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Selfwhere
    Self: PartialOrd<Self>,

Restrict a value to a certain interval.

impl<T, A> PartialEq<BTreeSet<T, A>> for BTreeSet<T, A>where
    T: PartialEq<T>,
    A: Allocator + Clone,

fn eq(&self, other: &BTreeSet<T, A>) -> bool

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

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

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

impl<T, A> PartialOrd<BTreeSet<T, A>> for BTreeSet<T, A>where
    T: PartialOrd<T>,
    A: Allocator + Clone,

fn partial_cmp(&self, other: &BTreeSet<T, A>) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

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

This method tests less than (for self and other) and is used by the < operator.

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

This method tests less than or equal to (for self and other) and is used by the <= operator.

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

This method tests greater than (for self and other) and is used by the > operator.

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

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl<T, A> Sub<&BTreeSet<T, A>> for &BTreeSet<T, A>where
    T: Ord + Clone,
    A: Allocator + Clone,

fn sub(self, rhs: &BTreeSet<T, A>) -> BTreeSet<T, A>

Returns the difference of self and rhs as a new BTreeSet<T>.

Examples

use std::collections::BTreeSet;

let a = BTreeSet::from([1, 2, 3]);
let b = BTreeSet::from([3, 4, 5]);

let result = &a - &b;
assert_eq!(result, BTreeSet::from([1, 2]));

type Output = BTreeSet<T, A>

The resulting type after applying the - operator.

impl<T, A> Eq for BTreeSet<T, A>where
    T: Eq,
    A: Allocator + Clone,