@thi.ng/associative

@thi.ng/associative

This project is part of the @thi.ng/umbrella monorepo.

About

This package provides alternative Set & Map data type implementations with customizable equality semantics, as well as common operations working with these types:

• Array based ArraySet, Linked List based LLSet, Skiplist based SortedMap & SortedSet and customizable EquivMap implement the full ES6 Map/Set APIs and additional features:
  • range query iterators (via entries(), keys(), values()) (sorted types only)
  • ICopy, IEmpty & IEquiv implementations
  • ICompare implementation for sorted types
  • multiple value additions / updates / deletions via into(), dissoc() (maps) and disj() (sets)
  • configurable key equality & comparison (incl. default implementations)
  • getters w/ optional "not-found" default value
  • fromObject() converters (for maps only)
• Polymorphic set operations (union, intersection, difference) - works with both native and custom Sets and retains their types
• Natural & selective joins (incl. key renaming, ported from Clojure)
• Key-value pair inversion for maps and vanilla objects
  • i.e. swaps K => V to V => K
• Single or multi-property index generation for maps and objects
• Key selection & renaming for maps and objects

Why?

The native ES6 implementations use object reference identity to determine key containment, but often it's more practical and useful to use equivalent value semantics for this purpose, especially when keys are structured data (arrays / objects).

Note: It's the user's responsibility to ensure the inserted keys are kept immutable (even if technically they're not).

Comparison with ES6 native types

// first two objects w/ equal values
a = [1, 2];
b = [1, 2];

Using native implementations

set = new Set();
set.add(a);
set.has(b);
// false

map = new Map();
map.set(a, "foo");
map.get(b);
// undefined

Using custom implementations:

import * as assoc from "@thi.ng/associative";

set = new assoc.ArraySet();
set.add(a);
set.add({a: 1});
// ArraySet { [ 1, 2 ], { a: 1 } }
set.has(b);
// true
set.has({a: 1});
// true

set = new assoc.LLSet();
set.add(a);
set.add({a: 1});
// LLSet { [ 1, 2 ], { a: 1 } }
set.has(b);
// true
set.has({a: 1});
// true

// by default EquivMap uses ArraySet for its canonical keys
map = new assoc.EquivMap();

// with custom implementation
map = new assoc.EquivMap(null, { keys: assoc.ArraySet });
map.set(a, "foo");
// EquivMap { [ 1, 2 ] => 'foo' }
map.get(b);
// "foo"

// Hash map w/ user supplied hash code function
// (here using `hash` function for arrays)
import { hash } from "@thi.ng/vectors"

m = new assoc.HashMap([], { hash })
m.set([1, 2], "a");
m.set([3, 4, 5], "b");
m.set([1, 2], "c");
// HashMap { [ 1, 2 ] => 'c', [ 3, 4, 5 ] => 'b' }

set = new assoc.SortedSet([a, [-1, 2], [-1, -2]]);
// SortedSet { [ -1, -2 ], [ -1, 2 ], [ 1, 2 ] }
set.has(b);
// true

map = new assoc.SortedMap([[a, "foo"], [[-1,-2], "bar"]]);
// SortedMap { [ -1, -2 ] => 'bar', [ 1, 2 ] => 'foo' }
map.get(b);
// "foo"

// key lookup w/ default value
map.get([3,4], "n/a");
// "n/a"

Installation

yarn add @thi.ng/associative

Dependencies

• @thi.ng/api
• @thi.ng/checks
• @thi.ng/compare
• @thi.ng/dcons
• @thi.ng/equiv
• @thi.ng/errors
• @thi.ng/transducers

Types

IEquivSet

All Set implementations in this package implement the IEquivSet interface, an extension of the native ES6 Set API.

ArraySet

Simple array based Set implementation which by default uses @thi.ng/equiv for value equivalence checking.

LLSet

Similar to ArraySet, but uses @thi.ng/dcons linked list as backing storage for values.

EquivMap

This Map implementation uses a native ES6 Map as backing storage for its key-value pairs and an additional IEquivSet implementation for canonical keys. By default uses ArraySet for this purpose.

HashMap

Map implementation w/ standard ES6 Map API, supporting any key type via hash codes computed via user supplied hash function. Uses Open Addressing / Linear Probing to resolve key collisions. Customizable via HashMapOpts constructor argument. Hash function MUST be given.

SortedMap

Alternative implementation of the ES6 Map API using a Skip list as backing store and support for configurable key equality and sorting semantics. Like with sets, uses @thi.ng/equiv & @thi.ng/compare by default.

William Pugh's (creator of this data structure) description:

"Skip lists are probabilistic data structures that have the same asymptotic expected time bounds as balanced trees, are simpler, faster and use less space."

Data structure description:

• ftp://ftp.cs.umd.edu/pub/skipLists/skiplists.pdf
• https://en.wikipedia.org/wiki/Skip_list

Ranged queries

map = new assoc.SortedMap([
    ["c", 3], ["a", 1], ["d", 4], ["b", 2]
]);
// SortedMap { 'a' => 1, 'b' => 2, 'c' => 3, 'd' => 4 }

// all entries
[...map.entries()]
// [ [ 'd', 4 ], [ 'c', 3 ], [ 'b', 2 ], [ 'a', 1 ] ]

// range query w/ given start key
// also works with `keys()` and `values()`
[...map.entries("c")]
// [ [ 'c', 3 ], [ 'd', 4 ] ]

// unknown start keys are ok
[...map.entries("cc")]
// [ [ 'd', 4 ] ]

// range query w/ given MAX key
[...map.entries("c", true)]
// [ [ 'a', 1 ], [ 'b', 2 ], [ 'c', 3 ] ]

SortedSet

Sorted set implementation with standard ES6 Set API, customizable value equality and comparison semantics and additional functionality:

• range queries (via entries, keys, values)
• multiple value addition/deletion via into() and disj()

Furthermore, this class implements the ICopy, IEmpty, ICompare and IEquiv interfaces defined by @thi.ng/api. The latter two allow instances to be used as keys themselves in other data types defined in this (and other) package(s).

This set uses a SortedMap as backing store.

Usage examples

Please see these packages for use cases:

• @thi.ng/cache
• @thi.ng/dgraph
• @thi.ng/rstream-query

Authors

• Karsten Schmidt

License

© 2017 - 2019 Karsten Schmidt // Apache Software License 2.0