pub struct HashSet<T, S = RandomState> { /* fields omitted */ }
An implementation of a hash set using the underlying representation of a HashMap where the value is ().
As with the HashMap
type, a HashSet
requires that the elements implement the Eq
and Hash
traits. This can frequently be achieved by using #[derive(PartialEq, Eq, Hash)]
. If you implement these yourself, it is important that the following property holds:
k1 == k2 -> hash(k1) == hash(k2)
In other words, if two keys are equal, their hashes must be equal.
It is a logic error for an item to be modified in such a way that the item's hash, as determined by the Hash
trait, or its equality, as determined by the Eq
trait, changes while it is in the set. This is normally only possible through Cell
, RefCell
, global state, I/O, or unsafe code.
use std::collections::HashSet; // Type inference lets us omit an explicit type signature (which // would be `HashSet<&str>` in this example). let mut books = HashSet::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); }
The easiest way to use HashSet
with a custom type is to derive Eq
and Hash
. We must also derive PartialEq
, this will in the future be implied by Eq
.
use std::collections::HashSet; #[derive(Hash, Eq, PartialEq, Debug)] struct Viking<'a> { name: &'a str, power: usize, } let mut vikings = HashSet::new(); vikings.insert(Viking { name: "Einar", power: 9 }); vikings.insert(Viking { name: "Einar", power: 9 }); vikings.insert(Viking { name: "Olaf", power: 4 }); vikings.insert(Viking { name: "Harald", power: 8 }); // Use derived implementation to print the vikings. for x in &vikings { println!("{:?}", x); }
HashSet with fixed list of elements can be initialized from an array:
use std::collections::HashSet; fn main() { let viking_names: HashSet<&str> = [ "Einar", "Olaf", "Harald" ].iter().cloned().collect(); // use the values stored in the set }
impl<T: Hash + Eq> HashSet<T, RandomState>
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fn new() -> HashSet<T, RandomState>
Creates an empty HashSet.
use std::collections::HashSet; let mut set: HashSet<i32> = HashSet::new();
fn with_capacity(capacity: usize) -> HashSet<T, RandomState>
Creates an empty HashSet
with the specified capacity.
The hash set will be able to hold at least capacity
elements without reallocating. If capacity
is 0, the hash set will not allocate.
use std::collections::HashSet; let mut set: HashSet<i32> = HashSet::with_capacity(10);
impl<T, S> HashSet<T, S> where T: Eq + Hash, S: BuildHasher
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fn with_hasher(hasher: S) -> HashSet<T, S>
Creates a new empty hash set which will use the given hasher to hash keys.
The hash set is also created with the default initial capacity.
Warning: hasher
is normally randomly generated, and is designed to allow HashSet
s to be resistant to attacks that cause many collisions and very poor performance. Setting it manually using this function can expose a DoS attack vector.
use std::collections::HashSet; use std::collections::hash_map::RandomState; let s = RandomState::new(); let mut set = HashSet::with_hasher(s); set.insert(2);
fn with_capacity_and_hasher(capacity: usize, hasher: S) -> HashSet<T, S>
Creates an empty HashSet with with the specified capacity, using hasher
to hash the keys.
The hash set will be able to hold at least capacity
elements without reallocating. If capacity
is 0, the hash set will not allocate.
Warning: hasher
is normally randomly generated, and is designed to allow HashSet
s to be resistant to attacks that cause many collisions and very poor performance. Setting it manually using this function can expose a DoS attack vector.
use std::collections::HashSet; use std::collections::hash_map::RandomState; let s = RandomState::new(); let mut set = HashSet::with_capacity_and_hasher(10, s); set.insert(1);
fn hasher(&self) -> &S
Returns a reference to the set's hasher.
fn capacity(&self) -> usize
Returns the number of elements the set can hold without reallocating.
use std::collections::HashSet; let set: HashSet<i32> = HashSet::with_capacity(100); assert!(set.capacity() >= 100);
fn reserve(&mut self, additional: usize)
Reserves capacity for at least additional
more elements to be inserted in the HashSet
. The collection may reserve more space to avoid frequent reallocations.
Panics if the new allocation size overflows usize
.
use std::collections::HashSet; let mut set: HashSet<i32> = HashSet::new(); set.reserve(10);
fn shrink_to_fit(&mut self)
Shrinks the capacity of the set as much as possible. It will drop down as much as possible while maintaining the internal rules and possibly leaving some space in accordance with the resize policy.
use std::collections::HashSet; let mut set = HashSet::with_capacity(100); set.insert(1); set.insert(2); assert!(set.capacity() >= 100); set.shrink_to_fit(); assert!(set.capacity() >= 2);
fn iter(&self) -> Iter<T>
An iterator visiting all elements in arbitrary order. Iterator element type is &'a T.
use std::collections::HashSet; let mut set = HashSet::new(); set.insert("a"); set.insert("b"); // Will print in an arbitrary order. for x in set.iter() { println!("{}", x); }
fn difference<'a>(&'a self, other: &'a HashSet<T, S>) -> Difference<'a, T, S>
Visit the values representing the difference.
use std::collections::HashSet; let a: HashSet<_> = [1, 2, 3].iter().cloned().collect(); let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect(); // Can be seen as `a - b`. for x in a.difference(&b) { println!("{}", x); // Print 1 } let diff: HashSet<_> = a.difference(&b).cloned().collect(); assert_eq!(diff, [1].iter().cloned().collect()); // Note that difference is not symmetric, // and `b - a` means something else: let diff: HashSet<_> = b.difference(&a).cloned().collect(); assert_eq!(diff, [4].iter().cloned().collect());
fn symmetric_difference<'a>(&'a self,
other: &'a HashSet<T, S>)
-> SymmetricDifference<'a, T, S>
Visit the values representing the symmetric difference.
use std::collections::HashSet; let a: HashSet<_> = [1, 2, 3].iter().cloned().collect(); let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect(); // Print 1, 4 in arbitrary order. for x in a.symmetric_difference(&b) { println!("{}", x); } let diff1: HashSet<_> = a.symmetric_difference(&b).cloned().collect(); let diff2: HashSet<_> = b.symmetric_difference(&a).cloned().collect(); assert_eq!(diff1, diff2); assert_eq!(diff1, [1, 4].iter().cloned().collect());
fn intersection<'a>(&'a self,
other: &'a HashSet<T, S>)
-> Intersection<'a, T, S>
Visit the values representing the intersection.
use std::collections::HashSet; let a: HashSet<_> = [1, 2, 3].iter().cloned().collect(); let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect(); // Print 2, 3 in arbitrary order. for x in a.intersection(&b) { println!("{}", x); } let intersection: HashSet<_> = a.intersection(&b).cloned().collect(); assert_eq!(intersection, [2, 3].iter().cloned().collect());
fn union<'a>(&'a self, other: &'a HashSet<T, S>) -> Union<'a, T, S>
Visit the values representing the union.
use std::collections::HashSet; let a: HashSet<_> = [1, 2, 3].iter().cloned().collect(); let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect(); // Print 1, 2, 3, 4 in arbitrary order. for x in a.union(&b) { println!("{}", x); } let union: HashSet<_> = a.union(&b).cloned().collect(); assert_eq!(union, [1, 2, 3, 4].iter().cloned().collect());
fn len(&self) -> usize
Returns the number of elements in the set.
use std::collections::HashSet; let mut v = HashSet::new(); assert_eq!(v.len(), 0); v.insert(1); assert_eq!(v.len(), 1);
fn is_empty(&self) -> bool
Returns true if the set contains no elements.
use std::collections::HashSet; let mut v = HashSet::new(); assert!(v.is_empty()); v.insert(1); assert!(!v.is_empty());
fn drain(&mut self) -> Drain<T>
Clears the set, returning all elements in an iterator.
fn clear(&mut self)
Clears the set, removing all values.
use std::collections::HashSet; let mut v = HashSet::new(); v.insert(1); v.clear(); assert!(v.is_empty());
fn contains<Q: ?Sized>(&self, value: &Q) -> bool where T: Borrow<Q>, Q: Hash + Eq
Returns true
if the set contains a value.
The value may be any borrowed form of the set's value type, but Hash
and Eq
on the borrowed form must match those for the value type.
use std::collections::HashSet; let set: HashSet<_> = [1, 2, 3].iter().cloned().collect(); assert_eq!(set.contains(&1), true); assert_eq!(set.contains(&4), false);
fn get<Q: ?Sized>(&self, value: &Q) -> Option<&T> where T: Borrow<Q>, Q: Hash + Eq
Returns a reference to the value in the set, if any, that is equal to the given value.
The value may be any borrowed form of the set's value type, but Hash
and Eq
on the borrowed form must match those for the value type.
fn is_disjoint(&self, other: &HashSet<T, S>) -> bool
Returns true
if the set has no elements in common with other
. This is equivalent to checking for an empty intersection.
use std::collections::HashSet; let a: HashSet<_> = [1, 2, 3].iter().cloned().collect(); let mut b = HashSet::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);
fn is_subset(&self, other: &HashSet<T, S>) -> bool
Returns true
if the set is a subset of another.
use std::collections::HashSet; let sup: HashSet<_> = [1, 2, 3].iter().cloned().collect(); let mut set = HashSet::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);
fn is_superset(&self, other: &HashSet<T, S>) -> bool
Returns true
if the set is a superset of another.
use std::collections::HashSet; let sub: HashSet<_> = [1, 2].iter().cloned().collect(); let mut set = HashSet::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);
fn insert(&mut self, value: T) -> bool
Adds a value to the set.
If the set did not have this value present, true
is returned.
If the set did have this value present, false
is returned.
use std::collections::HashSet; let mut set = HashSet::new(); assert_eq!(set.insert(2), true); assert_eq!(set.insert(2), false); assert_eq!(set.len(), 1);
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. Returns the replaced value.
fn remove<Q: ?Sized>(&mut self, value: &Q) -> bool where T: Borrow<Q>, Q: Hash + Eq
Removes a value from the set. Returns true
if the value was present in the set.
The value may be any borrowed form of the set's value type, but Hash
and Eq
on the borrowed form must match those for the value type.
use std::collections::HashSet; let mut set = HashSet::new(); set.insert(2); assert_eq!(set.remove(&2), true); assert_eq!(set.remove(&2), false);
fn take<Q: ?Sized>(&mut self, value: &Q) -> Option<T> where T: Borrow<Q>, Q: Hash + Eq
Removes and returns the value in the set, if any, that is equal to the given one.
The value may be any borrowed form of the set's value type, but Hash
and Eq
on the borrowed form must match those for the value type.
impl<T: Clone, S: Clone> Clone for HashSet<T, S>
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fn clone(&self) -> HashSet<T, S>
Returns a copy of the value. Read more
fn clone_from(&mut self, source: &Self)
Performs copy-assignment from source
. Read more
impl<T, S> PartialEq for HashSet<T, S> where T: Eq + Hash, S: BuildHasher
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fn eq(&self, other: &HashSet<T, S>) -> bool
This method tests for self
and other
values to be equal, and is used by ==
. Read more
fn ne(&self, other: &Rhs) -> bool
This method tests for !=
.
impl<T, S> Eq for HashSet<T, S> where T: Eq + Hash, S: BuildHasher
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impl<T, S> Debug for HashSet<T, S> where T: Eq + Hash + Debug, S: BuildHasher
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fn fmt(&self, f: &mut Formatter) -> Result
Formats the value using the given formatter.
impl<T, S> FromIterator<T> for HashSet<T, S> where T: Eq + Hash,
S: BuildHasher + Default
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fn from_iter<I: IntoIterator<Item=T>>(iter: I) -> HashSet<T, S>
Creates a value from an iterator. Read more
impl<T, S> Extend<T> for HashSet<T, S> where T: Eq + Hash, S: BuildHasher
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fn extend<I: IntoIterator<Item=T>>(&mut self, iter: I)
Extends a collection with the contents of an iterator. Read more
impl<'a, T, S> Extend<&'a T> for HashSet<T, S> where T: 'a + Eq + Hash + Copy,
S: BuildHasher
fn extend<I: IntoIterator<Item=&'a T>>(&mut self, iter: I)
Extends a collection with the contents of an iterator. Read more
impl<T, S> Default for HashSet<T, S> where T: Eq + Hash,
S: BuildHasher + Default
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fn default() -> HashSet<T, S>
Creates an empty HashSet<T, S>
with the Default
value for the hasher.
impl<'a, 'b, T, S> BitOr<&'b HashSet<T, S>> for &'a HashSet<T, S> where T: Eq + Hash + Clone,
S: BuildHasher + Default
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type Output = HashSet<T, S>
The resulting type after applying the |
operator
fn bitor(self, rhs: &HashSet<T, S>) -> HashSet<T, S>
Returns the union of self
and rhs
as a new HashSet<T, S>
.
use std::collections::HashSet; let a: HashSet<_> = vec![1, 2, 3].into_iter().collect(); let b: HashSet<_> = vec![3, 4, 5].into_iter().collect(); let set = &a | &b; let mut i = 0; let expected = [1, 2, 3, 4, 5]; for x in &set { assert!(expected.contains(x)); i += 1; } assert_eq!(i, expected.len());
impl<'a, 'b, T, S> BitAnd<&'b HashSet<T, S>> for &'a HashSet<T, S> where T: Eq + Hash + Clone,
S: BuildHasher + Default
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type Output = HashSet<T, S>
The resulting type after applying the &
operator
fn bitand(self, rhs: &HashSet<T, S>) -> HashSet<T, S>
Returns the intersection of self
and rhs
as a new HashSet<T, S>
.
use std::collections::HashSet; let a: HashSet<_> = vec![1, 2, 3].into_iter().collect(); let b: HashSet<_> = vec![2, 3, 4].into_iter().collect(); let set = &a & &b; let mut i = 0; let expected = [2, 3]; for x in &set { assert!(expected.contains(x)); i += 1; } assert_eq!(i, expected.len());
impl<'a, 'b, T, S> BitXor<&'b HashSet<T, S>> for &'a HashSet<T, S> where T: Eq + Hash + Clone,
S: BuildHasher + Default
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type Output = HashSet<T, S>
The resulting type after applying the ^
operator
fn bitxor(self, rhs: &HashSet<T, S>) -> HashSet<T, S>
Returns the symmetric difference of self
and rhs
as a new HashSet<T, S>
.
use std::collections::HashSet; let a: HashSet<_> = vec![1, 2, 3].into_iter().collect(); let b: HashSet<_> = vec![3, 4, 5].into_iter().collect(); let set = &a ^ &b; let mut i = 0; let expected = [1, 2, 4, 5]; for x in &set { assert!(expected.contains(x)); i += 1; } assert_eq!(i, expected.len());
impl<'a, 'b, T, S> Sub<&'b HashSet<T, S>> for &'a HashSet<T, S> where T: Eq + Hash + Clone,
S: BuildHasher + Default
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type Output = HashSet<T, S>
The resulting type after applying the -
operator
fn sub(self, rhs: &HashSet<T, S>) -> HashSet<T, S>
Returns the difference of self
and rhs
as a new HashSet<T, S>
.
use std::collections::HashSet; let a: HashSet<_> = vec![1, 2, 3].into_iter().collect(); let b: HashSet<_> = vec![3, 4, 5].into_iter().collect(); let set = &a - &b; let mut i = 0; let expected = [1, 2]; for x in &set { assert!(expected.contains(x)); i += 1; } assert_eq!(i, expected.len());
impl<'a, T, S> IntoIterator for &'a HashSet<T, S> where T: Eq + Hash,
S: BuildHasher
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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. Read more
impl<T, S> IntoIterator for HashSet<T, S> where T: Eq + Hash, S: BuildHasher
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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) -> IntoIter<T>
Creates a consuming iterator, that is, one that moves each value out of the set in arbitrary order. The set cannot be used after calling this.
use std::collections::HashSet; let mut set = HashSet::new(); set.insert("a".to_string()); set.insert("b".to_string()); // Not possible to collect to a Vec<String> with a regular `.iter()`. let v: Vec<String> = set.into_iter().collect(); // Will print in an arbitrary order. for x in &v { println!("{}", x); }
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Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/collections/struct.HashSet.html