Set2

This is a tiny library which exposes a javascript Set2 class. ES6 Sets only contain one element. If you try to put an array of to elements [a,b] into a set, you won't be able to set for membership because each time you use the literal list constructor, you make a new element! (Sets use reference equality, not deep equality).

So this is an itty bitty class which fixes that problem, exposing a Set-like API for tuples of elements (a,b).

The API is heavily based on the API for ES6 Sets. Use set2.add(a, b) to add an entry to a set, set2.has(a, b) to test for containment and set2.delete(a, b) to remove the entry again.

The Set2 API supports both set2.forEach and the new for (var e of set) { ... } syntax to iterate over sets. (e is an array of [a, b]).

This library depends on the javascript Map and Set class, so its avaliable in NodeJS 0.12, IoJS and any modern browser. Any polyfill that adds Map and Set to the global object should work fine too.

I made Set2 alongside Map2. You might find that class useful too.

Install it with:

% npm install set2

A quick tour:

var Set2 = require('set2');

var s = new Set2;
m.add(1, 2).add(3, 4); // Chainable!

m.has(1, 2); // true

var obj1 = {x:5};
var obj2 = ['an','array'];
m.add(obj1, obj2);

m.has(obj1, obj2); // true

m.size; // 2

// To delete things, you can either delete items individually:
m.delete(1, 2); // returns true if something was deleted.

// Or delete everything all at once:
m.clear();

// To iterate, either use .forEach():
m.forEach(function(a, b) {
  console.log(a, b); // Prints 1,2 and {x:5},['an','array'] 
});

// Or use the new es6 iterators.
for (var entry of m) {
  console.log(entry); // An array of [a, b]
}

API

Constructor

The Set2 constructor makes a new Set2 and optionally initializes it with data.

var Set2 = require('set2');
var set = new Set2;

Or with data:

var Set2 = require('set2');

// Equalivant of calling set.add(1,2); set.add(3,4);
var set = new Set2([[1,2], [3,4]]);

set.add(a, b)

Add the tuple (a, b) to the set. Add returns the set itself, so you can chain it.

set.add(1, 2).add(3, 4);

set.has(1, 2); // true

set.has(a, b)

Checks to see if the set contains (a, b). Note that sets use reference equality, so object literals with the same value aren't considered to be the same object.

set.add(1, 2);
set.has(1, 2); // true

var o1 = {}, o2 = {};
set.add(o1, o2);
set.has(o1, o2); // true

// But:
set.add({}, []);
set.has({}, []); // false because {} and [] make new objects.

set.delete(a, b)

Deletes the set entry (a, b). Returns true if an item was removed from the set, false otherwise.

set.deleteAll(a)

Delete all entries which are (a, anything).

set.clear()

Remove all objects from the set. After clear() is called, the object will have a size of 0.

set.size

The number of entries in the set.

set.size; // 0
set.add(1, 2); // 1
set.add(1, 2); // still 1
set.delete(1, 2); // 0

set.subset(a)

This is a convenience method for getting another set which contains all the b's for a given a value. The returned set is still used by Set2, so be careful editing the returned set or keeping a long lived reference.

Iterating

There are two ways to iterate through all the items in a Set2:

• Use set.forEach
• Use ES6 Iterators

I haven't done extensive performance testing, but until javascript iterators are better optimized, forEach is probably going to be faster. (Using a closure allocates a function, but using an iterator allocates an object for each iteration of the loop).

Its currently undefined what happens if you add new items to a set while iterating through it. (You may or may not see the new object). That said, removing the item you're currently iterating through is ok.

The order of iteration is not guaranteed. Do not depend on it in any way. (If you care about the order of your items, consider using an array instead).

set.forEach(function(a, b) {...})

Call set.forEach to iterate through the set with a custom iterator function.

set.add(1, 2, 3).add(3, 4);

set.forEach(function(value, key1, key2) {
  // Prints 1, 2, 3 and 4, 5, 6.
  console.log(key1, key2, value);
});

set.values()

Get an iterator for the entries in the set. Each entry in the result is an array of [key1, key2, value]. Set.entries is also exposed via set[Symbol.iterator] for usage in for..of loops.

set.add(1, 2);
set.add(3, 4);

for (var entry of set) {
  // Prints 1, 2 and 3, 4
  console.log(entry[0], entry[1]);
}

Or awkwardly from Coffeescript:

set.add 1, 2
set.add 3, 4

iter = set.entries()
while !(v = iter.next()).done
  [a, b] = v.value
  console.log a, b

From Coffeescript I recommend just sticking with set.forEach (a, b) -> ... until better syntax lands in coffeescript.

Set.values is also aliased as Set.entries and Set[Symbol.iterator] for convenience and API coherence.

License

Copyright (c) 2015, Joseph Gentle <[email protected]>

Permission to use, copy, modify, and/or distribute this software for any
purpose with or without fee is hereby granted, provided that the above
copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
PERFORMANCE OF THIS SOFTWARE.