WeightedRandom

A library for working with weighted randomness implementing Vose's Alias method.

Examples

Immutable Weighted Collection

A WeightedCollection does not allow you to modify the weights of the collection once it has been created.

Normalised

If you already have your item set probabilities normalised you can use the WeightedCollection constructor

var items = Set.of("A", "B", "C", "D");
var probs = List.of(.5d, .25d, .125d, .125d);
var wc = new WeightedCollection<String>(items, probs);

int[] t = new int[4];
for (int i = 0; i < ITER; i++) {
    switch (wc.next()) {
        case "A" -> t[0]++;
        case "B" -> t[1]++;
        case "C" -> t[2]++;
        case "D" -> t[3]++;
    }
}
System.out.println(Arrays.toString(t));

Additionally you can create a collection from a Map.

var items = new HashMap<String, Integer>();
items.put("A", .5d);
items.put("B", .25d);
items.put("C", .125d);
items.put("D", .125d);
var wc = new WeightedCollection<String>(items);

int[] t = new int[4];
for (int i = 0; i < ITER; i++) {
    switch (wc.next()) {
        case "A" -> t[0]++;
        case "B" -> t[1]++;
        case "C" -> t[2]++;
        case "D" -> t[3]++;
    }
}
System.out.println(Arrays.toString(t));

Unnormalised

If your values are unnormalised you can use the static factory methods to create an WeightedCollection from a Map.

You can do this from a Map containing Doubles or Integers.

var items = new HashMap<String, Double>();
items.put("A", 50d);
items.put("B", 25d);
items.put("C", 12.5d);
items.put("D", 12.5d);
var wc = WeightedCollection.fromUnnormalisedDoubleProbability(items);

int[] t = new int[4];
for (int i = 0; i < ITER; i++) {
    switch (wc.next()) {
        case "A" -> t[0]++;
        case "B" -> t[1]++;
        case "C" -> t[2]++;
        case "D" -> t[3]++;
    }
}
System.out.println(Arrays.toString(t));

var items = new HashMap<String, Integer>();
items.put("A", 100);
items.put("B", 50);
items.put("C", 25);
items.put("D", 25);
var wc = WeightedCollection.fromUnnormalisedIntegerProbability(items);

int[] t = new int[4];
for (int i = 0; i < ITER; i++) {
    switch (wc.next()) {
        case "A" -> t[0]++;
        case "B" -> t[1]++;
        case "C" -> t[2]++;
        case "D" -> t[3]++;
    }
}
System.out.println(Arrays.toString(t));