LinkedHashSet class - dart:collection library (original) (raw)
A LinkedHashSet is a hash-table based Set implementation.
The default implementation of Set is LinkedHashSet.
The LinkedHashSet also keeps track of the order that elements were inserted in, and iteration happens in first-to-last insertion order.
The elements of a LinkedHashSet must have consistent Object.==and Object.hashCode implementations. This means that the == operator must define a stable equivalence relation on the elements (reflexive, symmetric, transitive, and consistent over time), and that hashCodemust be the same for objects that are considered equal by ==.
Iteration of elements is done in element insertion order. An element that was added after another will occur later in the iteration. Adding an element that is already in the set does not change its position in the iteration order, but removing an element and adding it again will make it the last element of an iteration.
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.
**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 planets = <String>{}; // LinkedHashSet
To add data to a set, use add or addAll.
final uranusAdded = planets.add('Uranus'); // true
planets.addAll({'Venus', 'Mars', 'Earth', 'Jupiter'});
print(planets); // {Uranus, Venus, Mars, Earth, Jupiter}
To check if the set is empty, use isEmpty or isNotEmpty. To find the number of elements in the set, use length.
print(planets.isEmpty); // false
print(planets.length); // 5
To check whether the set has an element with a specific value, use contains.
final marsExists = planets.contains('Mars'); // true
The forEach method calls a function with each element of the set.
planets.forEach(print);
// Uranus
// Venus
// Mars
// Earth
// Jupiter
To make a copy of the set, use toSet.
final copySet = planets.toSet();
print(copySet); // {Uranus, Venus, Mars, Earth, Jupiter}
To remove an element, use remove.
final removedValue = planets.remove('Mars'); // Mars
print(planets); // {Uranus, Venus, Earth, Jupiter}
To remove multiple elements at the same time, use removeWhere orremoveAll.
planets.removeWhere((element) => element.startsWith('E'));
print(planets); // {Uranus, Venus, Jupiter}
To removes all elements in this set that do not meet a condition, use retainWhere.
planets.retainWhere((element) => element.contains('Jupiter'));
print(planets); // {Jupiter}
```dart continued
To remove all elements and empty the set, use [clear].
```dart continued
planets.clear();
print(planets.isEmpty); // true
print(planets); // {}
See also:
- Set is the general interface of collection where each object can occur only once.
- HashSet the order of the objects in the iteration is not guaranteed.
- SplayTreeSet iterates the objects in sorted order.
Implemented types
- Set<E>
Available extensions
Constructors
LinkedHashSet({bool equals(E, E)?, int hashCode(E)?, bool isValidKey(dynamic)?})
Create an insertion-ordered hash set using the providedequals and hashCode.
factory
LinkedHashSet.from(Iterable elements)
Create a linked hash set containing all elements.
factory
Creates an insertion-ordered identity-based set.
factory
LinkedHashSet.of(Iterable<E> elements)
Create a linked hash set from elements.
factory
Properties
first → E
The first element.
no setterinherited
firstOrNull → T?
Available on Iterable<T>, provided by the IterableExtensions extension
The first element of this iterator, or null if the iterable is empty.
no setter
The hash code for this object.
no setterinherited
Available on Iterable<T>, provided by the IterableExtensions extension
Pairs of elements of the indices and elements of this iterable.
no setter
Whether this collection has no elements.
no setterinherited
Whether this collection has at least one element.
no setterinherited
Provides an iterator that iterates over the elements in insertion order.
no setteroverride
last → E
The last element.
no setterinherited
lastOrNull → T?
Available on Iterable<T>, provided by the IterableExtensions extension
The last element of this iterable, or null if the iterable is empty.
no setter
The number of elements in this Iterable.
no setterinherited
Available on Iterable<T?>, provided by the NullableIterableExtensions extension
The non-null elements of this iterable.
no setter
A representation of the runtime type of the object.
no setterinherited
single → E
Checks that this iterable has only one element, and returns that element.
no setterinherited
singleOrNull → T?
Available on Iterable<T>, provided by the IterableExtensions extension
The single element of this iterator, or null.
no setter
Available on Iterable<Future<T>>, provided by the FutureIterable extension
Waits for futures in parallel.
no setter
Methods
Adds value to the set.
inherited
addAll(Iterable<E> elements)→ void
Adds all elements to this set.
inherited
any(bool test(E element))→ bool
Checks whether any element of this iterable satisfies test.
inherited
Available on Iterable<T>, provided by the EnumByName extension
Creates a map from the names of enum values to the values.
Available on Iterable<T>, provided by the EnumByName extension
Finds the enum value in this list with name name.
Provides a view of this set as a set of R instances.
inherited
clear()→ void
Removes all elements from the set.
inherited
Whether value is in the set.
inherited
containsAll(Iterable<Object?> other)→ bool
Whether this set contains all the elements of other.
inherited
difference(Set<Object?> other)→ Set<E>
Creates a new set with the elements of this that are not in other.
inherited
Returns the indexth element.
inherited
elementAtOrNull(int index)→ T?
Available on Iterable<T>, provided by the IterableExtensions extension
The element at position index of this iterable, or null.
every(bool test(E element))→ bool
Checks whether every element of this iterable satisfies test.
inherited
expand<T>(Iterable<T> toElements(E element))→ Iterable<T>
Expands each element of this Iterable into zero or more elements.
inherited
firstWhere(bool test(E element), {E orElse()?})→ E
The first element that satisfies the given predicate test.
inherited
fold<T>(T initialValue, T combine(T previousValue, E element))→ T
Reduces a collection to a single value by iteratively combining each element of the collection with an existing value
inherited
followedBy(Iterable<E> other)→ Iterable<E>
Creates the lazy concatenation of this iterable and other.
inherited
forEach(void action(E element))→ void
Executes a function on each element of the set.
override
intersection(Set<Object?> other)→ Set<E>
Creates a new set which is the intersection between this set and other.
inherited
join([String separator = ""])→ String
Converts each element to a String and concatenates the strings.
inherited
lastWhere(bool test(E element), {E orElse()?})→ E
The last element that satisfies the given predicate test.
inherited
If an object equal to object is in the set, return it.
inherited
map<T>(T toElement(E e))→ Iterable<T>
The current elements of this iterable modified by toElement.
inherited
noSuchMethod(Invocation invocation)→ dynamic
Invoked when a nonexistent method or property is accessed.
inherited
reduce(E combine(E value, E element))→ E
Reduces a collection to a single value by iteratively combining elements of the collection using the provided function.
inherited
Removes value from the set.
inherited
removeAll(Iterable<Object?> elements)→ void
Removes each element of elements from this set.
inherited
removeWhere(bool test(E element))→ void
Removes all elements of this set that satisfy test.
inherited
retainAll(Iterable<Object?> elements)→ void
Removes all elements of this set that are not elements in elements.
inherited
retainWhere(bool test(E element))→ void
Removes all elements of this set that fail to satisfy test.
inherited
singleWhere(bool test(E element), {E orElse()?})→ E
The single element that satisfies test.
inherited
Creates an Iterable that provides all but the first count elements.
inherited
skipWhile(bool test(E value))→ Iterable<E>
Creates an Iterable that skips leading elements while test is satisfied.
inherited
Creates a lazy iterable of the count first elements of this iterable.
inherited
takeWhile(bool test(E value))→ Iterable<E>
Creates a lazy iterable of the leading elements satisfying test.
inherited
toList({bool growable = true})→ List<E>
Creates a List containing the elements of this Iterable.
inherited
Creates a Set with the same elements and behavior as this Set.
inherited
A string representation of this object.
inherited
Creates a new set which contains all the elements of this set and other.
inherited
where(bool test(E element))→ Iterable<E>
Creates a new lazy Iterable with all elements that satisfy the predicate test.
inherited
Creates a new lazy Iterable with all elements that have type T.
inherited
Operators
operator ==(Object other)→ bool
The equality operator.
inherited