https://github.com/pschiffmann/indexed-set.dart

Provides an `IndexedSet` class, an implementation of `Set` that computes an index for each of its elements, and exposes this mapping through the `[]` operator.
https://github.com/pschiffmann/indexed-set.dart

Last synced: 8 months ago
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Provides an `IndexedSet` class, an implementation of `Set` that computes an index for each of its elements, and exposes this mapping through the `[]` operator.

• Host: GitHub
• URL: https://github.com/pschiffmann/indexed-set.dart
• Owner: pschiffmann
• License: mit
• Created: 2017-09-20T23:20:01.000Z (over 8 years ago)
• Default Branch: master
• Last Pushed: 2018-11-10T19:40:19.000Z (over 7 years ago)
• Last Synced: 2025-10-23T02:59:45.205Z (8 months ago)
• Language: Dart
• Homepage: https://pub.dartlang.org/packages/indexed_set
• Size: 51.8 KB
• Stars: 2
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGELOG.md
  • License: LICENSE

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README

          
Dart indexed set

================

[![Build Status](https://travis-ci.com/pschiffmann/indexed-set.dart.svg?branch=master)](https://travis-ci.com/pschiffmann/indexed-set.dart)

This package provides an `IndexedSet` class, and a pair of `Superset`/`Subset` classes that implement the `IndexedSet` interface.

IndexedSet

----------

An `IndexedSet` adds a mapping mechanism to the `Set` interface.

A user-provided function `I index(E element)` calculates an index for each element.

The elements are then accessible through the `[]` operator.

This allows you to define cleaner APIs than if you used a `Map`, because the data structure can enforce integrity of the key/value mapping.

```dart

enum System { frontend, backend }

class Account {

  final String name;

  final System system;

  Account(this.name, this.system);

  String toString() => '$system-account of $name';

}

/// Supports lookup of accounts by username.

final frontendAccounts = new IndexedSet(

    (Account acc) => acc.name,

    isValidElement: (Account acc) => acc.system == System.frontend);

```

Superset / Subset

-----------------

Both `Superset` and `Subset` are indexed sets that use `int` as the index type.

A Superset is immutable and stores its elements in ascending order -- the first element will have index `0`, the last element index `set.length - 1`.

A Subset has to be taken from a superset, and can only contain elements that are also contained in the superset.

The idea was that subsets could store their elements in a bit vector, which would be very space-efficient, and time-efficient for set operations (difference, intersection, union) on subsets of the same superset. However, `Subset` is outperformed by a regular `HashSet` in most situations.