1 package net.bmahe.genetics4j.core.replacement;
2
3 import java.util.Comparator;
4 import java.util.List;
5 import java.util.stream.IntStream;
6
7 import org.apache.commons.lang3.Validate;
8
9 import net.bmahe.genetics4j.core.Genotype;
10 import net.bmahe.genetics4j.core.Population;
11 import net.bmahe.genetics4j.core.selection.Selector;
12 import net.bmahe.genetics4j.core.spec.AbstractEAConfiguration;
13 import net.bmahe.genetics4j.core.spec.replacement.DeleteNLast;
14
15 public class DeleteNLastImpl<T extends Comparable<T>> implements ReplacementStrategyImplementor<T> {
16
17 private final DeleteNLast deleteNLastSpec;
18 private final Selector<T> offspringSelector;
19
20 public DeleteNLastImpl(final DeleteNLast _deleteNLastSpec, final Selector<T> _offspringSelector) {
21 Validate.notNull(_deleteNLastSpec);
22 Validate.notNull(_offspringSelector);
23
24 this.deleteNLastSpec = _deleteNLastSpec;
25 this.offspringSelector = _offspringSelector;
26 }
27
28 @Override
29 public Population<T> select(final AbstractEAConfiguration<T> eaConfiguration, final int numIndividuals,
30 final List<Genotype> population, final List<T> populationScores, final List<Genotype> offsprings,
31 final List<T> offspringScores) {
32 Validate.notNull(eaConfiguration);
33 Validate.isTrue(numIndividuals > 0);
34 Validate.notNull(population);
35 Validate.notNull(populationScores);
36 Validate.isTrue(population.size() == populationScores.size());
37 Validate.notNull(offsprings);
38 Validate.notNull(offspringScores);
39 Validate.isTrue(offsprings.size() == offspringScores.size());
40
41 final Comparator<T> populationComparator = eaConfiguration.fitnessComparator();
42
43 final Population<T> selected = new Population<>();
44
45 final int weakestN = (int) (numIndividuals * deleteNLastSpec.weakRatio());
46
47 IntStream.range(0, populationScores.size())
48 .boxed()
49 .sorted((a, b) -> populationComparator.compare(populationScores.get(a), populationScores.get(b)))
50 .skip(weakestN)
51 .forEach(index -> {
52 selected.add(population.get(index), populationScores.get(index));
53 });
54
55 final Population<T> selectedOffspring = offspringSelector
56 .select(eaConfiguration, weakestN, offsprings, offspringScores);
57 selected.addAll(selectedOffspring);
58
59 return selected;
60 }
61 }