source: java/ecj/cecj/archive/ArchiveRandomSelection.java

/*
  Copyright 2009 by Marcin Szubert
  Licensed under the Academic Free License version 3.0
 */

package cecj.archive;

import java.util.List;

import ec.EvolutionState;
import ec.Individual;
import ec.SelectionMethod;
import ec.select.SelectDefaults;
import ec.util.Parameter;

public class ArchiveRandomSelection extends SelectionMethod {

        /** default base */
        private static final String P_ARCHIVAL_RANDOM = "archival-random";

        private static final String P_SIZE = "size";
        private static final int ENTIRE_ARCHIVE = -1;

        private int size;

        public Parameter defaultBase() {
                return SelectDefaults.base().push(P_ARCHIVAL_RANDOM);
        }

        @Override
        public void setup(EvolutionState state, Parameter base) {
                super.setup(state, base);
                
                Parameter sizeParam = base.push(P_SIZE);
                size = state.parameters.getIntWithDefault(sizeParam, null, ENTIRE_ARCHIVE);
        }

        @Override
        public int produce(int subpopulation, EvolutionState state, int thread) {
                throw new UnsupportedOperationException(
                        "Archival selection methods do not support supopulation index-based produce method.");
        }

        @Override
        public int produce(int min, int max, int start, int subpop, Individual[] inds,
                        EvolutionState state, int thread) {
                int n = 1;
                if (n > max)
                        n = max;
                if (n < min)
                        n = min;

                List<Individual> archive = ((ArchivingSubpopulation) state.population.subpops[subpop])
                        .getArchivalIndividuals();
                List<Individual> popInds = ((ArchivingSubpopulation) state.population.subpops[subpop])
                        .getIndividuals();

                if (!archive.isEmpty()) {
                        for (int q = 0; q < n; q++) {
                                int selected;
                                if (size <= 0) {
                                        selected = state.random[thread].nextInt(archive.size());
                                } else {
                                        selected = archive.size() - state.random[thread].nextInt(size) - 1;
                                        selected = Math.max(selected, 0);
                                }
                                inds[start + q] = archive.get(selected);
                        }
                } else {
                        for (int q = 0; q < n; q++) {
                                inds[start + q] = popInds.get(state.random[thread].nextInt(popInds.size()));
                        }
                }

                return n;
        }
}