hyracks/hyracks-storage-am-lsm-invertedindex/src/main/java/org/apache/hyracks/storage/am/lsm/invertedindex/search/JaccardSearchModifier.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.hyracks.storage.am.lsm.invertedindex.search;

import org.apache.hyracks.storage.am.lsm.invertedindex.api.IInvertedIndexSearchModifier;

public class JaccardSearchModifier implements IInvertedIndexSearchModifier {

    private float jaccThresh;

    public JaccardSearchModifier(float jaccThresh) {
        this.jaccThresh = jaccThresh;
    }

    @Override
    public int getOccurrenceThreshold(int numQueryTokens) {
        return Math.max((int) Math.floor((float) numQueryTokens * jaccThresh), 1);
    }

    @Override
    public int getNumPrefixLists(int occurrenceThreshold, int numInvLists) {
        if (numInvLists == 0) {
            return 0;
        }
        return numInvLists - occurrenceThreshold + 1;
    }

    @Override
    public short getNumTokensLowerBound(short numQueryTokens) {
        return (short) Math.floor(numQueryTokens * jaccThresh);
    }

    @Override
    public short getNumTokensUpperBound(short numQueryTokens) {
        return (short) Math.ceil(numQueryTokens / jaccThresh);
    }

    public float getJaccThresh() {
        return jaccThresh;
    }

    public void setJaccThresh(float jaccThresh) {
        this.jaccThresh = jaccThresh;
    }

    @Override
    public String toString() {
        return "Jaccard Search Modifier, Threshold: " + jaccThresh;
    }
}