Struct std::collections::HashSet1.0.0 [] [src]

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.

Examples

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);
}Run

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);
}Run

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
}Run

Methods

impl<T: Hash + Eq> 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.

Examples

use std::collections::HashSet;
let set: HashSet<i32> = HashSet::new();Run

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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.

Examples

use std::collections::HashSet;
let set: HashSet<i32> = HashSet::with_capacity(10);
assert!(set.capacity() >= 10);Run

impl<T, S> HashSet<T, S> where
    T: Eq + Hash,
    S: BuildHasher
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1.7.0
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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.

Examples

use std::collections::HashSet;
use std::collections::hash_map::RandomState;

let s = RandomState::new();
let mut set = HashSet::with_hasher(s);
set.insert(2);Run

1.7.0
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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.

Examples

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);Run

1.9.0
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Returns a reference to the set's BuildHasher.

Examples

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();Run

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Returns the number of elements the set can hold without reallocating.

Examples

use std::collections::HashSet;
let set: HashSet<i32> = HashSet::with_capacity(100);
assert!(set.capacity() >= 100);Run

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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

Panics if the new allocation size overflows usize.

Examples

use std::collections::HashSet;
let mut set: HashSet<i32> = HashSet::new();
set.reserve(10);
assert!(set.capacity() >= 10);Run

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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.

Examples

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);Run

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An iterator visiting all elements in arbitrary order. The iterator element type is &'a T.

Examples

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);
}Run

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Visits the values representing the difference, i.e. the values that are in self but not in other.

Examples

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());Run

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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.

Examples

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());Run

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Visits the values representing the intersection, i.e. the values that are both in self and other.

Examples

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());Run

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Visits the values representing the union, i.e. all the values in self or other, without duplicates.

Examples

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());Run

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Returns the number of elements in the set.

Examples

use std::collections::HashSet;

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

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Returns true if the set contains no elements.

Examples

use std::collections::HashSet;

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

1.6.0
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Clears the set, returning all elements in an iterator.

Examples

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());Run

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Clears the set, removing all values.

Examples

use std::collections::HashSet;

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

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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.

Examples

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);Run

1.9.0
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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.

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

Examples

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);Run

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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.

Examples

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);Run

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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.

Examples

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);Run

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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.

Examples

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);Run

1.9.0
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Adds a value to the set, replacing the existing value, if any, that is equal to the given one. Returns the replaced value.

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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.

Examples

use std::collections::HashSet;

let mut set = HashSet::new();

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

1.9.0
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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.

1.18.0
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Retains only the elements specified by the predicate.

In other words, remove all elements e such that f(&e) returns false.

Examples

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);Run

Trait Implementations

impl<T: Clone, S: Clone> Clone for HashSet<T, S>
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Returns a copy of the value. Read more

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

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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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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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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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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
1.4.0
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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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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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The resulting type after applying the | operator.

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Returns the union of self and rhs as a new HashSet<T, S>.

Examples

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());Run

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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The resulting type after applying the | operator.

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Returns the union of self and rhs as a new HashSet<T, S>.

Examples

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());Run

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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The resulting type after applying the & operator.

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Returns the intersection of self and rhs as a new HashSet<T, S>.

Examples

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());Run

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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The resulting type after applying the & operator.

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Returns the intersection of self and rhs as a new HashSet<T, S>.

Examples

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());Run

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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The resulting type after applying the ^ operator.

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Returns the symmetric difference of self and rhs as a new HashSet<T, S>.

Examples

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());Run

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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The resulting type after applying the ^ operator.

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Returns the symmetric difference of self and rhs as a new HashSet<T, S>.

Examples

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());Run

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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The resulting type after applying the - operator.

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Returns the difference of self and rhs as a new HashSet<T, S>.

Examples

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());Run

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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The resulting type after applying the - operator.

[src]

Returns the difference of self and rhs as a new HashSet<T, S>.

Examples

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());Run

impl<'a, T, S> IntoIterator for &'a HashSet<T, S> where
    T: Eq + Hash,
    S: BuildHasher
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The type of the elements being iterated over.

Which kind of iterator are we turning this into?

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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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The type of the elements being iterated over.

Which kind of iterator are we turning this into?

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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.

Examples

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);
}Run