如何使用加权函数对多个字段的搜索结果进行排序？

Question

我有一个Lucene索引,其中每个文档都有几个包含数值的字段.现在我想在这个字段的加权和上对搜索结果进行排序.例如:

field1=100
field2=002
field3=014

加权函数看起来像:

f(d) = field1 * 0.5 + field2 * 1.4 + field3 * 1.8

结果应按表示文档的f(d)位置排序d.排序功能应该是非静态的,并且可能因搜索到搜索而不同,因为常量因素受执行搜索的用户的影响.

有谁知道如何解决这个问题,或者想知道如何以另一种方式实现这一目标？

Answer 1

您可以尝试实现自定义ScoreDocComparator.例如:

public class ScaledScoreDocComparator implements ScoreDocComparator {

    private int[][] values;
    private float[] scalars;

    public ScaledScoreDocComparator(IndexReader reader, String[] fields, float[] scalars) throws IOException {
        this.scalars = scalars;
        this.values = new int[fields.length][];
        for (int i = 0; i < values.length; i++) {
            this.values[i] = FieldCache.DEFAULT.getInts(reader, fields[i]);
        }
    }

    protected float score(ScoreDoc scoreDoc) {
        int doc = scoreDoc.doc;

        float score = 0;
        for (int i = 0; i < values.length; i++) {
            int value = values[i][doc];
            float scalar = scalars[i];
            score += (value * scalar);
        }
        return score;
    }

    @Override
    public int compare(ScoreDoc i, ScoreDoc j) {
        float iScore = score(i);
        float jScore = score(j);
        return Float.compare(iScore, jScore);
    }

    @Override
    public int sortType() {
        return SortField.CUSTOM;
    }

    @Override
    public Comparable<?> sortValue(ScoreDoc i) {
        float score = score(i);
        return Float.valueOf(score);
    }

}

这是一个实际的例子ScaledScoreDocComparator.我相信它适用于我的测试,但我鼓励您根据您的数据进行证明.

final String[] fields = new String[]{ "field1", "field2", "field3" };
final float[] scalars = new float[]{ 0.5f, 1.4f, 1.8f };

Sort sort = new Sort(
    new SortField(
        "",
        new SortComparatorSource() {
            public ScoreDocComparator newComparator(IndexReader reader, String fieldName) throws IOException {
                return new ScaledScoreDocComparator(reader, fields, scalars);
            }
        }
    )
);

IndexSearcher indexSearcher = ...;
Query query = ...;
Filter filter = ...; // can be null
int nDocs = 100;

TopFieldDocs topFieldDocs = indexSearcher.search(query, filter, nDocs, sort);
ScoreDoc[] scoreDocs = topFieldDocs.scoreDocs;

奖金!

似乎Lucene开发人员正在弃用该ScoreDocComparator接口(它目前在Subversion存储库中已被弃用).这是一个ScaledScoreDocComparator修改为坚持ScoreDocComparator继承者的例子,FieldComparator:

public class ScaledComparator extends FieldComparator {

    private String[] fields;
    private float[] scalars;
    private int[][] slotValues;
    private int[][] currentReaderValues;
    private int bottomSlot;

    public ScaledComparator(int numHits, String[] fields, float[] scalars) {
        this.fields = fields;
        this.scalars = scalars;

        this.slotValues = new int[this.fields.length][];
        for (int fieldIndex = 0; fieldIndex < this.fields.length; fieldIndex++) {
            this.slotValues[fieldIndex] = new int[numHits];
        }

        this.currentReaderValues = new int[this.fields.length][];
    }

    protected float score(int[][] values, int secondaryIndex) {
        float score = 0;

        for (int fieldIndex = 0; fieldIndex < fields.length; fieldIndex++) {
            int value = values[fieldIndex][secondaryIndex];
            float scalar = scalars[fieldIndex];
            score += (value * scalar);
        }

        return score;
    }

    protected float scoreSlot(int slot) {
        return score(slotValues, slot);
    }

    protected float scoreDoc(int doc) {
        return score(currentReaderValues, doc);
    }

    @Override
    public int compare(int slot1, int slot2) {
        float score1 = scoreSlot(slot1);
        float score2 = scoreSlot(slot2);
        return Float.compare(score1, score2);
    }

    @Override
    public int compareBottom(int doc) throws IOException {
        float bottomScore = scoreSlot(bottomSlot);
        float docScore = scoreDoc(doc);
        return Float.compare(bottomScore, docScore);
    }

    @Override
    public void copy(int slot, int doc) throws IOException {
        for (int fieldIndex = 0; fieldIndex < fields.length; fieldIndex++) {
            slotValues[fieldIndex][slot] = currentReaderValues[fieldIndex][doc];
        }
    }

    @Override
    public void setBottom(int slot) {
        bottomSlot = slot;
    }

    @Override
    public void setNextReader(IndexReader reader, int docBase, int numSlotsFull) throws IOException {
        for (int fieldIndex = 0; fieldIndex < fields.length; fieldIndex++) {
            String field = fields[fieldIndex];
            currentReaderValues[fieldIndex] = FieldCache.DEFAULT.getInts(reader, field);
        }
    }

    @Override
    public int sortType() {
        return SortField.CUSTOM;
    }

    @Override
    public Comparable<?> value(int slot) {
        float score = scoreSlot(slot);
        return Float.valueOf(score);
    }

}

使用这个新类与原始类非常相似,只是sort对象的定义有点不同:

final String[] fields = new String[]{ "field1", "field2", "field3" };
final float[] scalars = new float[]{ 0.5f, 1.4f, 1.8f };

Sort sort = new Sort(
    new SortField(
        "",
        new FieldComparatorSource() {
            public FieldComparator newComparator(String fieldname, int numHits, int sortPos, boolean reversed) throws IOException {
                return new ScaledComparator(numHits, fields, scalars);
            }
        }
    )
);