Note: the rand crate now has built-in-support for the Alias method, so this library is no longer needed.

A Rust implementation of roulette wheel selection using the Alias Method. This can be used to simulate a loaded die and similar situations.

Initialization takes O(n) time; choosing a random element takes O(1) time. This is far faster than naive algorithms (the most common of which is commonly known as 'roulette wheel selection'). For an in-depth explanation of the algorithm, see http://www.keithschwarz.com/darts-dice-coins/.

This code was translated from http://www.keithschwarz.com/interesting/code/?dir=alias-method.

Example

Run example with cargo run --example simple

extern crate rand;
extern crate roulette;

use roulette::Roulette;

fn main() {
  let mut rng = rand::thread_rng();
  let roulette = Roulette::new(vec![
      ('a', 1.0), ('b', 1.0), ('c', 0.5), ('d', 0.0)]);
  for _ in 0..10 {
      let rand = roulette.sample(&mut rng);
      println!("{}", rand);
  }
}

In this example, rand will be 'a' with 40% probability, 'b' with 40% probability, and 'c' with 20% probability.