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Implementation of various string similarity and distance algorithms: Levenshtein, Jaro-winkler, n-Gram, Q-Gram, Jaccard index, Longest Common Subsequence edit distance, cosine similarity...

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/*
 * The MIT License
 *
 * Copyright 2015 tibo.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

package info.debatty.java.utils;

import java.io.Serializable;
import java.util.HashMap;
import java.util.SortedSet;
import java.util.TreeSet;

/**
 *
 * @author tibo
 */
public class SparseBooleanVector implements Serializable {
    
    /** 
     * Indicates the positions that hold the value "true"
     */
    protected int[] keys;

    public SparseBooleanVector(int size) {
        keys = new int[size];
    }
    
    public SparseBooleanVector() {
        this(20);
    }
    
    public SparseBooleanVector(HashMap hashmap) {
        this(hashmap.size());
        SortedSet sorted_keys = new TreeSet(hashmap.keySet());
        int size = 0;
        for (int key : sorted_keys) {
            keys[size] = key;
            size++;
        }
    }

    /**
     * 
     * @param array 
     */
    public SparseBooleanVector(boolean[] array) {
        
        int size = 0;
        for (int i = 0; i < array.length; i++) {
            if (array[i]) {
                size++;
            }
        }
        
        keys = new int[size];
        int j = 0;
        for (int i = 0; i < array.length; i++) {
            if (array[i]) {
                keys[j] = i;
                j++;
            }
        }
    }
    
    
    /**
     * Computes and return the Jaccard index with other SparseVector.
     * |A inter B| / |A union B|
     * It is actually computed as |A inter B| / (|A| +|B| - | A inter B|)
     * using a single loop over A and B
     * @param other
     * @return 
     */
    public double jaccard(SparseBooleanVector other) {
        int intersection = this.intersection(other);
        return (double) intersection / (this.size() + other.size() - intersection);
    }
    
    /**
     * 
     * @param other
     * @return 
     */
    public int union(SparseBooleanVector other) {
        return this.size() + other.size() - this.intersection(other);
    }
    
    /**
     * 
     * @param other
     * @return 
     */
    public int intersection(SparseBooleanVector other) {
        int agg = 0;
        int i = 0;
        int j = 0;
        while (i < this.keys.length  && j < other.keys.length) {
            int k1 = this.keys[i];
            int k2 = other.keys[j];

            if (k1 == k2) {
                agg++;
                i++;
                j++;

            } else if (k1 < k2) {
                i++;
                
            } else {
                j++;
            }
        }
        return agg;
    }
    
    @Override
    public String toString() {
        String r = "";
        for (int i = 0; i < size(); i++) {
            r += keys[i] + ":" + keys[i] + " ";
        }
        
        return r;
    }

    /**
     * Return the number of (non-zero) elements in this vector.
     * @return 
     */
    public int size() {
        return this.keys.length;
    }
}