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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.metrics;

import com.google.common.base.Function;
import com.google.common.collect.Lists;
import org.grouplens.lenskit.eval.traintest.TestUser;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import java.io.IOException;
import java.util.List;

/**
 * A simple metric base class that tracks the current evaluation.
 *
 * @param  The context type.
 * @param  The type of per-user results.  This is a plain Java class that has fields or methods
 *           annotated with {@link ResultColumn} containing the per-user output columns.
 * @param  The type of global results.  This is a plain Java class that has fields or methods
 *           annotated with {@link ResultColumn} containing the aggregate output columns.
 *
 * @author GroupLens Research
 * @since 0.10
 */
public abstract class AbstractMetric implements Metric {
    private final ResultConverter aggregateConverter;
    private final ResultConverter userConverter;

    protected AbstractMetric(Class aggregate, Class user) {
        aggregateConverter = ResultConverter.create(aggregate);
        userConverter = ResultConverter.create(user);
    }

    /**
     * A prefix to be applied to column names.  If non-{@code null}, this prefix will be applied and
     * separated with a period.
     * @return The prefix to apply to column names.
     */
    protected String getPrefix() {
        return null;
    }

    /**
     * A suffix to be applied to column names.  If non-{@code null}, this suffix will be applied and
     * separated with a period.
     * @return The suffix to apply to column names.
     */
    protected String getSuffix() {
        return null;
    }

    @Override
    public List getColumnLabels() {
        return Lists.transform(aggregateConverter.getColumnLabels(), new HeaderTransform());
    }

    @Override
    public List getUserColumnLabels() {
        return Lists.transform(userConverter.getColumnLabels(), new HeaderTransform());
    }

    @Nonnull
    @Override
    public List