shikaga / socialchoice

Experimenting with voting systems

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SocialChoice

A playground for exploring vote counting methods.

• This document is available nicely formatted here.
• Tests are here.
• Source code is here.
• Demo is here.
• You can also get it with the following command if you're using node.

    npm install git+http://github.com/kybernetikos/SocialChoice.git#gh-pages

Getting Started

You can set up an election with the following code:

	var SocialChoice = require('SocialChoice');

	var vote = new SocialChoice({
		options: ["a", "b", "c", "d", "x", "y"]
	});

Options must have a unique toString.

Now you can vote for some of the options. Voting can be done by ranking, or by assigning a score, or by 'approving' some options. If you have a restriction that you can only approve a single option then this becomes a simple plurality election.

	vote.rank(10, ["a", "x"], "b");
	vote.rank(4, ["a", "x"], ["c", "y"]);
	vote.rank(2, "d", ["a", "x"], ["c", "y"], "b");
	vote.rank(19, ["c", "y"], "b", ["a", "x"]);

	vote.score(4, {
		"a": 3,
		"x": 99,
		"y": 52
	});

	vote.approve(3, "a", "y", "b");

You can get various kinds of results:

		console.log(vote.getSumResult());

		var r = vote.getRankingResult();
		console.log("ranked pairs", r.rankedPairs().join(" "));

		var i = vote.getRunOffResult();
		console.log("instant run-off", i.ranks.join(" "));

The whole system is very flexible and extensible. You can apply restrictions which check votes are valid for the particular election you are running, and ballot transforms which can modify votes.

A default restriction (called noWriteIns) is applied when you specify options in your configuration, which stops votes from ranking things not specified in the configured options.

A common ballot transform used by default (called missing) scores anything not mentioned in a ballot as 0 or ranks it last.

Some of the result objects have parameters too, for example it's possible to change the way the ranked pairs algorithm determines which pair-wise contests are most significant by passing a function parameter.