/**
* Method to select individuals from population. Selects the best N individuals.
*
* <p>Roulette wheel selection: If Fi is the fitness of individual i in the population, its
* probability of being selected is Pi = (Fi/sum of all the fitness in population)
*
* @param count The number of individuals to be selected
* @return List of selected individuals
*/
public List<AbstractIndividual> selectIndividuals(int count) {
ArrayList<AbstractIndividual> selected = new ArrayList<>();
Random r = new Random();
// find best individual and calculate the sum of individuals' fitnesses
AbstractIndividual best = this.individuals[0];
double totalFitness = 0.0;
for (AbstractIndividual individual : this.individuals) {
totalFitness += individual.getFitness();
if (individual.getFitness() > best.getFitness()) {
best = individual;
}
}
int index;
while (selected.size() < count) {
while (true) {
index = (r.nextInt(individuals.length));
if (r.nextDouble() < (individuals[index].getFitness() / totalFitness)) {
break;
}
}
selected.add(individuals[index]);
}
/**
* Tournament selection. we split the population into N groups of individuals and we pick the
* best one out of each group.
*/
/*
int split = individuals.length / count;
for(int i = 0; i < count; i++) {
AbstractIndividual best = this.individuals[split * i];
for (int j = (split * i); j < (split * (i + 1)); j++) {
if (individuals[j].getFitness() > best.getFitness() && !selected.contains(individuals[j])) {
best = individuals[j];
}
}
selected.add(best);
}
*/
/**
* elitism: select the best N individuals.
*
* <p>Doesn't work well, leads to premature convergence.
*/
/*
while (selected.size() < count) {
AbstractIndividual best = this.individuals[0];
for (AbstractIndividual individual : this.individuals) {
if (individual.getFitness() > best.getFitness() && !selected.contains(individual)) {
best = individual;
}
}
selected.add(best);
}
*/
/** Random selection. Primitive, doesn't work well */
/*
Random r = new Random();
AbstractIndividual individual = individuals[r.nextInt(individuals.length)];
while (selected.size() < count) {
selected.add(individual);
individual = individuals[r.nextInt(individuals.length)];
}
*/
return selected;
}
