SwiftSchulze

The Schulze method is a ranked-choice voting algorithm. It guarantees that a majority-preferred candidate wins when one exists. Preference cycles are resolved using transitive beatpaths: if A defeats B and B defeats C, then A indirectly defeats C.

https://en.wikipedia.org/wiki/Schulze_method

Installation

Requirements

You need Swift 6.2 or later installed on your system. To install Swift, visit:

https://www.swift.org/install

Clone the Repository

git clone https://github.com/uberbruns/SwiftSchulze.git
cd SwiftSchulze

Using the Command Line Tool

Run Directly

You can run the tool directly without building using:

swift run schulze --help

Build for Release

To build an optimized release binary:

swift build -c release

The compiled binary will be located at:

.build/release/schulze

You can then copy it to a location in your PATH:

cp .build/release/schulze /usr/local/bin/

Using the Library in Your App

If you want to use the Schulze algorithm in your Swift application, add this package as a dependency in your Package.swift:

dependencies: [
  .package(url: "https://github.com/uberbruns/SwiftSchulze.git", from: "0.1.0")
]

Then add SchulzeLibrary to your target dependencies:

.target(
  name: "YourTarget",
  dependencies: [
    .product(name: "SchulzeLibrary", package: "SwiftSchulze")
  ]
)

Import and use in your code:

import SchulzeLibrary

let rankings = [
  ["Alice", "Bob", "Charlie"],
  ["Bob", "Charlie", "Alice"],
  ["Charlie", "Alice", "Bob"]
]

let winner = Schulze.ranking(rankings: rankings)
print(winner)

Command Line Usage

OVERVIEW: Tool for calculating the winner of an election by letting voters cast
their vote in form of a ranked list of candidates.

USAGE: schulze [--ranking <ranking> ...] [--format <format>] [--stdin] [--path <path>] [--directory <directory>]

OPTIONS:
  -r, --ranking <ranking> A comma separated ranking of candidates casted by one
                          voter. Repeat this option for every participant.
  -f, --format <format>   The output format ('plain' or 'json'). (default:
                          plain)
  -s, --stdin             Takes a list of votes from standard input. Every line
                          should contain a comma separated ranking.
  -p, --path <path>       Use this option to provide a path to a file
                          containing the casted rankings. Every line should
                          contain the candidates ranked by one voter seperated
                          via comma.
  -d, --directory <directory>
                          Use this option to provide a directory containing
                          .txt files. Every file should contain the candidates
                          ranked by one voter. One candidate per line.
  -h, --help              Show help information.

License

This project is released under the MIT license. See LICENSE for details.