HashSet<E> class
An unordered hash-table based Set implementation.
The elements of a HashSet must have consistent equality and hashCode implementations. This means that the equals operation must define a stable equivalence relation on the elements (reflexive, symmetric, transitive, and consistent over time), and that the hashCode must be consistent with equality, so that it's the same for objects that are considered equal.
Most simple operations on HashSet are done in (potentially amortized) constant time: add, contains, remove, and length, provided the hash codes of objects are well distributed.
The iteration order of the set is not specified and depends on the hashcodes of the provided elements. However, the order is stable: multiple iterations over the same set produce the same order, as long as the set is not modified.
Note: Do not modify a set (add or remove elements) while an operation is being performed on that set, for example in functions called during a forEach or containsAll call, or while iterating the set.
Do not modify elements in a way which changes their equality (and thus their hash code) while they are in the set. Some specialized kinds of sets may be more permissive with regards to equality, in which case they should document their different behavior and restrictions.
Example:
final letters = HashSet<String>();
To add data to a set, use add or addAll.
letters.add('A');
letters.addAll({'B', 'C', 'D'});
To check if the set is empty, use isEmpty or isNotEmpty. To find the number of elements in the set, use length.
print(letters.isEmpty); // false
print(letters.length); // 4
print(letters); // fx {A, D, C, B}
To check whether the set has an element with a specific value, use contains.
final bExists = letters.contains('B'); // true
The forEach method calls a function with each element of the set.
letters.forEach(print); // A // D // C // B
To make a copy of the set, use toSet.
final anotherSet = letters.toSet();
print(anotherSet); // fx {A, C, D, B}
To remove an element, use remove.
final removedValue = letters.remove('A'); // true
print(letters); // fx {B, C, D}
To remove multiple elements at the same time, use removeWhere or removeAll.
letters.removeWhere((element) => element.startsWith('B'));
print(letters); // fx {D, C}
To removes all elements in this set that do not meet a condition, use retainWhere.
letters.retainWhere((element) => element.contains('C'));
print(letters); // {C}
To remove all elements and empty the set, use clear.
letters.clear();
print(letters.isEmpty); // true
print(letters); // {}
See also:
- Set is the general interface of collection where each object can occur only once.
- LinkedHashSet objects stored based on insertion order.
- SplayTreeSet iterates the objects in sorted order.
- Implemented types
-
- Set<
E>
- Set<
- Available Extensions
Constructors
-
HashSet({
bool equals(E, E)?,
int hashCode(E)?,
bool isValidKey(dynamic)?})
factory
-
Create a hash set using the provided
equalsas equality. -
HashSet.from(
Iterable elements)
factory
-
Create a hash set containing all
elements. -
HashSet.identity()
factory
- Creates an unordered identity-based set.
-
HashSet.of(
Iterable<
E> elements) factory -
Create a hash set containing all
elements.
Properties
-
first → E
read-only, inherited
- Returns the first element.
-
hashCode →
int
read-only, inherited
- The hash code for this object.
-
isEmpty →
bool
read-only, inherited
- Whether this collection has no elements.
-
isNotEmpty →
bool
read-only, inherited
- Whether this collection has at least one element.
-
iterator →
Iterator<
E> read-only, override - Provides an iterator that iterates over the elements of this set.
-
last → E
read-only, inherited
- Returns the last element.
-
length →
int
read-only, inherited
- Returns the number of elements in the iterable.
-
runtimeType →
Type
read-only, inherited
- A representation of the runtime type of the object.
-
single → E
read-only, inherited
- Checks that this iterable has only one element, and returns that element.
Methods
-
add(
E value) → bool inherited -
Adds
valueto the set. -
addAll(
Iterable< E> elements) → void inherited -
Adds all
elementsto this set. -
any(
bool test(E element)) → bool inherited -
Checks whether any element of this iterable satisfies
test. -
cast<
R>( ) → Set< R> inherited -
Provides a view of this set as a set of
Rinstances. -
clear(
) → void inherited - Removes all elements from the set.
-
contains(
Object? value) → bool inherited -
Whether
valueis in the set. -
containsAll(
Iterable< Object?> other) → bool inherited -
Whether this set contains all the elements of
other. -
difference(
Set< Object?> other) → Set< E> inherited -
Creates a new set with the elements of this that are not in
other. -
elementAt(
int index) → E inherited -
Returns the
indexth element. -
every(
bool test(E element)) → bool inherited -
Checks whether every element of this iterable satisfies
test. -
expand<
T>( Iterable< T> toElements(E element)) → Iterable< T> inherited - Expands each element of this Iterable into zero or more elements.
-
firstWhere(
bool test(E element), {E orElse()?}) → E inherited -
Returns the first element that satisfies the given predicate
test. -
fold<
T>( T initialValue, T combine(T previousValue, E element)) → T inherited - Reduces a collection to a single value by iteratively combining each element of the collection with an existing value
-
followedBy(
Iterable< E> other) → Iterable< E> inherited -
Returns the lazy concatenation of this iterable and
other. -
forEach(
void action(E element)) → void inherited -
Invokes
actionon each element of this iterable in iteration order. -
intersection(
Set< Object?> other) → Set< E> inherited -
Creates a new set which is the intersection between this set and
other. -
join(
[ String separator = ""]) → String inherited - Converts each element to a String and concatenates the strings.
-
lastWhere(
bool test(E element), {E orElse()?}) → E inherited -
Returns the last element that satisfies the given predicate
test. -
lookup(
Object? object) → E? inherited -
If an object equal to
objectis in the set, return it. -
map<
T>( T toElement(E e)) → Iterable< T> inherited -
The current elements of this iterable modified by
toElement. -
noSuchMethod(
Invocation invocation) → dynamic inherited - Invoked when a non-existent method or property is accessed.
-
reduce(
E combine(E value, E element)) → E inherited - Reduces a collection to a single value by iteratively combining elements of the collection using the provided function.
-
remove(
Object? value) → bool inherited -
Removes
valuefrom the set. -
removeAll(
Iterable< Object?> elements) → void inherited -
Removes each element of
elementsfrom this set. -
removeWhere(
bool test(E element)) → void inherited -
Removes all elements of this set that satisfy
test. -
retainAll(
Iterable< Object?> elements) → void inherited -
Removes all elements of this set that are not elements in
elements. -
retainWhere(
bool test(E element)) → void inherited -
Removes all elements of this set that fail to satisfy
test. -
singleWhere(
bool test(E element), {E orElse()?}) → E inherited -
Returns the single element that satisfies
test. -
skip(
int count) → Iterable< E> inherited -
Returns an
Iterable that provides all but the first
countelements. -
skipWhile(
bool test(E value)) → Iterable< E> inherited -
Returns an
Iterablethat skips leading elements whiletestis satisfied. -
take(
int count) → Iterable< E> inherited -
Returns a lazy iterable of the
countfirst elements of this iterable. -
takeWhile(
bool test(E value)) → Iterable< E> inherited -
Returns a lazy iterable of the leading elements satisfying
test. -
toList(
{ bool growable = true}) → List< E> inherited - Creates a List containing the elements of this Iterable.
-
toSet(
) → Set< E> inherited -
Creates a
Set with the same elements and behavior as this
Set. -
toString(
) → String inherited - A string representation of this object.
-
union(
Set< E> other) → Set< E> inherited -
Creates a new set which contains all the elements of this set and
other. -
where(
bool test(E element)) → Iterable< E> inherited -
Returns a new lazy
Iterable with all elements that satisfy the predicate
test. -
whereType<
T>( ) → Iterable< T> inherited -
Returns a new lazy
Iterable with all elements that have type
T.
Operators
-
operator ==(
Object other) → bool inherited - The equality operator.
© 2012 the Dart project authors
Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
https://api.dart.dev/stable/2.17.0/dart-collection/HashSet-class.html
