Posts Tagged ‘similarity’

Statistics on the similarity algorithms

July 27, 2010

So, just under a month ago I posted the following on similarity algorithms.

I have found it quite interesting to see which have been viewed, and the percentage share. Initially Damerau Levenshtein was the hot favourite, but then N-gram started coming through the ranks and is a clear leader with a 39% share of the hits!

I thought I would put together a simple histogram of the percentage share of hit for each similarity posting:

Disappointed my favourite, Markov chains, is languishing so far back…

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Java example of Jaro Winkler

June 28, 2010

This algorithm is purposely designed for record linkage, it was designed for linking short strings. It calculates a normalised score on the similarity between two strings.

The calculation is based on the number of matching characters held within the string and the number of transpositions.

The wikipedia entry can be found here, the other source was lingpipe:


public class JaroWinkler
{
    private String compOne;
    private String compTwo;

    private String theMatchA = "";
    private String theMatchB = "";
    private int mRange = -1;
    
    public JaroWinkler()
    {
    }
    
    public JaroWinkler(String s1, String s2)
    {
        compOne = s1;
        compTwo = s2;
    }

    public double getSimilarity(String s1, String s2)
    {
        compOne = s1;
        compTwo = s2;

        mRange = Math.max(compOne.length(), compTwo.length()) / 2 - 1;
        
        double res = -1;

        int m = getMatch();
        int t = 0;
        if (getMissMatch(compTwo,compOne) > 0)
        {
            t = (getMissMatch(compOne,compTwo) / getMissMatch(compTwo,compOne));
        }

        int l1 = compOne.length();
        int l2 = compTwo.length();

        double f = 0.3333;
        double mt = (double)(m-t)/m;
        double jw = f * ((double)m/l1+(double)m/l2+(double)mt);
        res = jw + getCommonPrefix(compOne,compTwo) * (0.1*(1.0 - jw));
        
        return res;
    }

    private int getMatch()
    {
        
        theMatchA = "";
        theMatchB = "";
        
        int matches = 0;

        for (int i = 0; i < compOne.length(); i++)
        {
            //Look backward
            int counter = 0;
            while(counter <= mRange && i >= 0 && counter <= i)
            {
                if (compOne.charAt(i) == compTwo.charAt(i - counter))
                {
                    matches++;
                    theMatchA = theMatchA + compOne.charAt(i);
                    theMatchB = theMatchB + compTwo.charAt(i);
                }
                counter++;                
            }

            //Look forward
            counter = 1;
            while(counter <= mRange && i < compTwo.length() && counter + i < compTwo.length())
            {
                if (compOne.charAt(i) == compTwo.charAt(i + counter))
                {
                    matches++;
                    theMatchA = theMatchA + compOne.charAt(i);
                    theMatchB = theMatchB + compTwo.charAt(i);
                }
                counter++;
            }
        }
        return matches;
    }

    private int getMissMatch(String s1, String s2)
    {
        int transPositions = 0;

        for (int i = 0; i < theMatchA.length(); i++)
        {
            //Look Backward
            int counter = 0;
            while(counter <= mRange && i >= 0 && counter <= i)
            {
                if (theMatchA.charAt(i) == theMatchB.charAt(i - counter) && counter > 0)
                {
                    transPositions++;
                }
                counter++;
            }

            //Look forward
            counter = 1;
            while(counter <= mRange && i < theMatchB.length() && (counter + i) < theMatchB.length())
            {
                if (theMatchA.charAt(i) == theMatchB.charAt(i + counter) && counter > 0)
                {
                    transPositions++;
                }
                counter++;
            }
        }
        return transPositions;
    }

    private int getCommonPrefix(String compOne, String compTwo)
    {
        int cp = 0;
        for (int i = 0; i < 4; i++)
        {
            if (compOne.charAt(i) == compTwo.charAt(i)) cp++;
        }
        return cp;
    }
}