DeleteNLastImpl.java
package net.bmahe.genetics4j.core.replacement;
import java.util.Comparator;
import java.util.List;
import java.util.stream.IntStream;
import org.apache.commons.lang3.Validate;
import net.bmahe.genetics4j.core.Genotype;
import net.bmahe.genetics4j.core.Population;
import net.bmahe.genetics4j.core.selection.Selector;
import net.bmahe.genetics4j.core.spec.AbstractEAConfiguration;
import net.bmahe.genetics4j.core.spec.replacement.DeleteNLast;
public class DeleteNLastImpl<T extends Comparable<T>> implements ReplacementStrategyImplementor<T> {
private final DeleteNLast deleteNLastSpec;
private final Selector<T> offspringSelector;
public DeleteNLastImpl(final DeleteNLast _deleteNLastSpec, final Selector<T> _offspringSelector) {
Validate.notNull(_deleteNLastSpec);
Validate.notNull(_offspringSelector);
this.deleteNLastSpec = _deleteNLastSpec;
this.offspringSelector = _offspringSelector;
}
@Override
public Population<T> select(final AbstractEAConfiguration<T> eaConfiguration, final int numIndividuals,
final List<Genotype> population, final List<T> populationScores, final List<Genotype> offsprings,
final List<T> offspringScores) {
Validate.notNull(eaConfiguration);
Validate.isTrue(numIndividuals > 0);
Validate.notNull(population);
Validate.notNull(populationScores);
Validate.isTrue(population.size() == populationScores.size());
Validate.notNull(offsprings);
Validate.notNull(offspringScores);
Validate.isTrue(offsprings.size() == offspringScores.size());
final Comparator<T> populationComparator = eaConfiguration.fitnessComparator();
final Population<T> selected = new Population<>();
final int weakestN = (int) (numIndividuals * deleteNLastSpec.weakRatio());
IntStream.range(0, populationScores.size())
.boxed()
.sorted((a, b) -> populationComparator.compare(populationScores.get(a), populationScores.get(b)))
.skip(weakestN)
.forEach(index -> {
selected.add(population.get(index), populationScores.get(index));
});
final Population<T> selectedOffspring = offspringSelector
.select(eaConfiguration, weakestN, offsprings, offspringScores);
selected.addAll(selectedOffspring);
return selected;
}
}