## Archive for the ‘Jaro Winkler’ Category

### 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;
}
}

```