pub struct HashSet<T, S = RandomState> { /* fields omitted */ }
A hash set implemented as 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);
} A 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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pub fn new() -> HashSet<T, RandomState>
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Creates an empty HashSet.
The hash set is initially created with a capacity of 0, so it will not allocate until it is first inserted into.
use std::collections::HashSet; let set: HashSet<i32> = HashSet::new();
pub fn with_capacity(capacity: usize) -> HashSet<T, RandomState>
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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 set: HashSet<i32> = HashSet::with_capacity(10); assert!(set.capacity() >= 10);
impl<T, S> HashSet<T, S> where
T: Eq + Hash,
S: BuildHasher,
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pub 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 HashSets 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);
pub 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 HashSets 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);
pub fn hasher(&self) -> &S
Returns a reference to the set's BuildHasher.
use std::collections::HashSet; use std::collections::hash_map::RandomState; let hasher = RandomState::new(); let set: HashSet<i32> = HashSet::with_hasher(hasher); let hasher: &RandomState = set.hasher();
pub fn capacity(&self) -> usize
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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);
pub fn reserve(&mut self, additional: usize)
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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); assert!(set.capacity() >= 10);
pub fn shrink_to_fit(&mut self)
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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);
pub fn iter(&self) -> Iter<T>
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An iterator visiting all elements in arbitrary order. The 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);
} pub fn difference<'a>(
&'a self,
other: &'a HashSet<T, S>
) -> Difference<'a, T, S>
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Visits the values representing the difference, i.e. the values that are in self but not in other.
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).collect();
assert_eq!(diff, [1].iter().collect());
// Note that difference is not symmetric,
// and `b - a` means something else:
let diff: HashSet<_> = b.difference(&a).collect();
assert_eq!(diff, [4].iter().collect()); pub fn symmetric_difference<'a>(
&'a self,
other: &'a HashSet<T, S>
) -> SymmetricDifference<'a, T, S>
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Visits the values representing the symmetric difference, i.e. the values that are in self or in other but not in both.
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).collect();
let diff2: HashSet<_> = b.symmetric_difference(&a).collect();
assert_eq!(diff1, diff2);
assert_eq!(diff1, [1, 4].iter().collect()); pub fn intersection<'a>(
&'a self,
other: &'a HashSet<T, S>
) -> Intersection<'a, T, S>
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Visits the values representing the intersection, i.e. the values that are both in self and other.
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).collect();
assert_eq!(intersection, [2, 3].iter().collect()); pub fn union<'a>(&'a self, other: &'a HashSet<T, S>) -> Union<'a, T, S>
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Visits the values representing the union, i.e. all the values in self or other, without duplicates.
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).collect();
assert_eq!(union, [1, 2, 3, 4].iter().collect()); pub fn len(&self) -> usize
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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);
pub fn is_empty(&self) -> bool
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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());
pub fn drain(&mut self) -> Drain<T>
Clears the set, returning all elements in an iterator.
use std::collections::HashSet;
let mut set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
assert!(!set.is_empty());
// print 1, 2, 3 in an arbitrary order
for i in set.drain() {
println!("{}", i);
}
assert!(set.is_empty()); pub fn clear(&mut self)
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Clears the set, removing all values.
use std::collections::HashSet; let mut v = HashSet::new(); v.insert(1); v.clear(); assert!(v.is_empty());
pub fn contains<Q: ?Sized>(&self, value: &Q) -> bool where
T: Borrow<Q>,
Q: Hash + Eq,
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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);
pub 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.
pub fn is_disjoint(&self, other: &HashSet<T, S>) -> bool
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Returns true if self 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);
pub fn is_subset(&self, other: &HashSet<T, S>) -> bool
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Returns true if the set is a subset of another, i.e. other contains at least all the values in self.
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);
pub fn is_superset(&self, other: &HashSet<T, S>) -> bool
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Returns true if the set is a superset of another, i.e. self contains at least all the values in other.
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);
pub fn insert(&mut self, value: T) -> bool
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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);
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. Returns the replaced value.
pub fn remove<Q: ?Sized>(&mut self, value: &Q) -> bool where
T: Borrow<Q>,
Q: Hash + Eq,
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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);
pub 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.
pub fn retain<F>(&mut self, f: F) where
F: FnMut(&T) -> bool,
Retains only the elements specified by the predicate.
In other words, remove all elements e such that f(&e) returns false.
use std::collections::HashSet; let xs = [1,2,3,4,5,6]; let mut set: HashSet<isize> = xs.iter().cloned().collect(); set.retain(|&k| k % 2 == 0); assert_eq!(set.len(), 3);
impl<T: Clone, S: Clone> Clone for HashSet<T, S>
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fn clone(&self) -> HashSet<T, S>
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Returns a copy of the value. Read more
fn clone_from(&mut self, source: &Self)
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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
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This method tests for self and other values to be equal, and is used by ==. Read more
fn ne(&self, other: &Rhs) -> bool
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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
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Formats the value using the given formatter. Read more
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>
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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)
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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)
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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>
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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>
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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>
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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>
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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>
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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 TThe 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>
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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 = TThe 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>
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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);
}
© 2010 The Rust Project Developers
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