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Facilities for evaluating recommender algorithms.
There is a newer version: 3.0-T5
/*
 * LensKit, an open source recommender systems toolkit.
 * Copyright 2010-2014 LensKit Contributors.  See CONTRIBUTORS.md.
 * Work on LensKit has been funded by the National Science Foundation under
 * grants IIS 05-34939, 08-08692, 08-12148, and 10-17697.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 51
 * Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */
package org.grouplens.lenskit.eval.traintest;

import org.grouplens.lenskit.eval.metrics.Metric;

import java.io.IOException;
import java.util.List;

/**
 * Create a metric for a train-test evaluation.  This interface allows a metric to control
 * its instantiation and lifecycle.
 *
 * @author GroupLens Research
 * @since 2.1
 */
public abstract class MetricFactory {
    public abstract Metric createMetric(TrainTestEvalTask task) throws IOException;

    public abstract List getColumnLabels();

    public abstract List getUserColumnLabels();

    /**
     * Create a metric factory that returns the provided pre-instantiated metric.
     * @param m The metric.
     * @return A metric factory that returns {@code m}.
     */
    public static  MetricFactory forMetric(Metric m) {
        return new Preinstantiated(m);
    }

    /**
     * Create a metric factory that wraps a class.  The class is instantiated immediately.
     * @param m The metric class.
     * @return A metric factory that returns {@code m}.
     */
    public static  MetricFactory forMetricClass(Class> m) {
        try {
            return new Preinstantiated(m.newInstance());
        } catch (InstantiationException e) {
            throw new RuntimeException("cannot instantiate " + m, e);
        } catch (IllegalAccessException e) {
            throw new RuntimeException("cannot instantiate " + m, e);
        }
    }

    private static class Preinstantiated extends MetricFactory {
        private final Metric metric;

        private Preinstantiated(Metric m) {
            this.metric = m;
        }

        @Override
        public Metric createMetric(TrainTestEvalTask task) {
            return metric;
        }

        @Override
        public List getColumnLabels() {
            return metric.getColumnLabels();
        }

        @Override
        public List getUserColumnLabels() {
            return metric.getUserColumnLabels();
        }
    }
}