Struct std::collections::HashSet
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pub struct HashSet<T, S = RandomState> {
// some 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.
Examples
fn main() { 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); } }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); }
Methods
impl<T: Hash + Eq> HashSet<T, RandomState>
fn new() -> HashSet<T, RandomState>
Creates an empty HashSet.
Examples
fn main() { use std::collections::HashSet; let mut set: HashSet<i32> = HashSet::new(); }use std::collections::HashSet; let mut set: HashSet<i32> = HashSet::new();
fn with_capacity(capacity: usize) -> HashSet<T, RandomState>
Creates an empty HashSet with space for at least n elements in
the hash table.
Examples
fn main() { use std::collections::HashSet; let mut set: HashSet<i32> = HashSet::with_capacity(10); }use std::collections::HashSet; let mut set: HashSet<i32> = HashSet::with_capacity(10);
impl<T, S> HashSet<T, S> where T: Eq + Hash, S: HashState
fn with_hash_state(hash_state: 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.
Examples
#![feature(hashmap_hasher)] fn main() { use std::collections::HashSet; use std::collections::hash_map::RandomState; let s = RandomState::new(); let mut set = HashSet::with_hash_state(s); set.insert(2); }#![feature(hashmap_hasher)] use std::collections::HashSet; use std::collections::hash_map::RandomState; let s = RandomState::new(); let mut set = HashSet::with_hash_state(s); set.insert(2);
fn with_capacity_and_hash_state(capacity: usize, hash_state: S) -> HashSet<T, S>
Creates an empty HashSet with space for at least capacity
elements in the hash table, using hasher to hash the keys.
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.
Examples
#![feature(hashmap_hasher)] fn main() { use std::collections::HashSet; use std::collections::hash_map::RandomState; let s = RandomState::new(); let mut set = HashSet::with_capacity_and_hash_state(10, s); set.insert(1); }#![feature(hashmap_hasher)] use std::collections::HashSet; use std::collections::hash_map::RandomState; let s = RandomState::new(); let mut set = HashSet::with_capacity_and_hash_state(10, s); set.insert(1);
fn capacity(&self) -> usize
Returns the number of elements the set can hold without reallocating.
Examples
fn main() { use std::collections::HashSet; let set: HashSet<i32> = HashSet::with_capacity(100); assert!(set.capacity() >= 100); }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
Panics if the new allocation size overflows usize.
Examples
fn main() { use std::collections::HashSet; let mut set: HashSet<i32> = HashSet::new(); set.reserve(10); }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.
Examples
fn main() { 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); }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.
Examples
fn main() { 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); } }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.
Examples
fn main() { 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()); }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.
Examples
fn main() { 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()); }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.
Examples
fn main() { 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()); }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.
Examples
fn main() { 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()); }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.
Examples
fn main() { use std::collections::HashSet; let mut v = HashSet::new(); assert_eq!(v.len(), 0); v.insert(1); assert_eq!(v.len(), 1); }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.
Examples
fn main() { use std::collections::HashSet; let mut v = HashSet::new(); assert!(v.is_empty()); v.insert(1); assert!(!v.is_empty()); }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.
Examples
fn main() { use std::collections::HashSet; let mut v = HashSet::new(); v.insert(1); v.clear(); assert!(v.is_empty()); }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.
Examples
fn main() { 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); }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
Unstable (
set_recovery #28050)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.
Examples
fn main() { 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); }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.
Examples
fn main() { 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); }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.
Examples
fn main() { 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); }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 a value present, true is returned.
If the set did have this key present, false is returned.
Examples
fn main() { 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); }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>
Unstable (
set_recovery #28050)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.
Examples
fn main() { use std::collections::HashSet; let mut set = HashSet::new(); set.insert(2); assert_eq!(set.remove(&2), true); assert_eq!(set.remove(&2), false); }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
Unstable (
set_recovery #28050)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.