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/*===============================================================================
 * Copyright (c) 2010-2012 University of Massachusetts.  All Rights Reserved.
 *
 * Use of the RankLib package is subject to the terms of the software license set
 * forth in the LICENSE file included with this software, and also available at
 * http://people.cs.umass.edu/~vdang/ranklib_license.html
 *===============================================================================
 */

package ciir.umass.edu.metric;

import java.util.Arrays;

import ciir.umass.edu.learning.RankList;

/**
 * @author vdang
 */
public class ReciprocalRankScorer extends MetricScorer {

    public ReciprocalRankScorer() {
        this.k = 0;//consider the whole list
    }

    @Override
    public double score(final RankList rl) {
        final int size = (rl.size() > k) ? k : rl.size();
        int firstRank = -1;
        for (int i = 0; i < size && (firstRank == -1); i++) {
            if (rl.get(i).getLabel() > 0.0) {
                firstRank = i + 1;
            }
        }
        return (firstRank == -1) ? 0 : (1.0f / firstRank);
    }

    @Override
    public MetricScorer copy() {
        return new ReciprocalRankScorer();
    }

    @Override
    public String name() {
        return "RR@" + k;
    }

    @Override
    public double[][] swapChange(final RankList rl) {
        int firstRank = -1;
        int secondRank = -1;
        final int size = (rl.size() > k) ? k : rl.size();
        for (int i = 0; i < size; i++) {
            if (rl.get(i).getLabel() > 0.0)//relevant
            {
                if (firstRank == -1) {
                    firstRank = i;
                } else if (secondRank == -1) {
                    secondRank = i;
                }
            }
        }

        //compute the change in RR by swapping each pair
        final double[][] changes = new double[rl.size()][];
        for (int i = 0; i < rl.size(); i++) {
            changes[i] = new double[rl.size()];
            Arrays.fill(changes[i], 0);
        }

        double rr = 0.0;
        //consider swapping the first rank doc with everything else further down the list
        if (firstRank != -1) {
            rr = 1.0 / (firstRank + 1);
            for (int j = firstRank + 1; j < size; j++) {
                if (((int) (rl.get(j).getLabel())) == 0)//non-relevant
                {
                    if (secondRank == -1 || j < secondRank) {
                        changes[firstRank][j] = changes[j][firstRank] = 1.0 / (j + 1) - rr;
                    } else {
                        changes[firstRank][j] = changes[j][firstRank] = 1.0 / (secondRank + 1) - rr;
                    }
                }
            }
            for (int j = size; j < rl.size(); j++) {
                if (((int) (rl.get(j).getLabel())) == 0)//non-relevant
                {
                    if (secondRank == -1) {
                        changes[firstRank][j] = changes[j][firstRank] = -rr;
                    } else {
                        changes[firstRank][j] = changes[j][firstRank] = 1.0 / (secondRank + 1) - rr;
                    }
                }
            }
        } else {
            firstRank = size;
        }

        //now it's time to consider swapping docs at earlier ranks than the first rank with those below it (and *it* too)
        for (int i = 0; i < firstRank; i++) {
            for (int j = firstRank; j < rl.size(); j++) {
                if (rl.get(j).getLabel() > 0) {
                    changes[i][j] = changes[j][i] = 1.0 / (i + 1) - rr;
                }
            }
        }
        return changes;
    }
}