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package com.wcohen.ss;
import com.wcohen.ss.api.*;
/**
* Winkler's reweighting scheme for distance metrics. In the
* literature, this was applied to the Jaro metric ('An Application of
* the Fellegi-Sunter Model of Record Linkage to the 1990
* U.S. Decennial Census' by William E. Winkler and Yves Thibaudeau.)
*/
public class WinklerRescorer extends AbstractStringDistance
{
private StringDistance innerDistance;
/** Rescore the innerDistance's scores, to account for the
* subjectively greater importance of the first few characters.
* <p>
* Note: the innerDistance must produce scores between 0 and 1.
*/
public WinklerRescorer(StringDistance innerDistance) { this.innerDistance = innerDistance; }
public String toString() { return "[WinklerRescorer:"+innerDistance+"]"; }
public double score(StringWrapper s,StringWrapper t)
{
double dist = innerDistance.score(s,t);
if (dist<0 || dist>1)
throw new IllegalArgumentException("innerDistance should produce scores between 0 and 1");
int prefLength = commonPrefixLength(4,s.unwrap(),t.unwrap());
dist = dist + prefLength*0.1 * (1 - dist);
return dist;
}
public String explainScore(StringWrapper s, StringWrapper t)
{
double dist = innerDistance.score(s,t);
int prefLength = commonPrefixLength(4,s.unwrap(),t.unwrap());
dist = dist + prefLength*0.1 * (1 - dist);
StringBuffer buf = new StringBuffer("");
buf.append("original score using "+innerDistance+":\n");
buf.append(innerDistance.explainScore(s,t)+"\n");
buf.append("prefLength = max(4,commonPrefixLength) = "+prefLength+"\n");
buf.append("Corrected score = dist + "+prefLength+"/10 * (1-dist) = "+score(s,t)+"\n");
return buf.toString();
}
private static int commonPrefixLength(int maxLength,String common1,String common2)
{
int n = Math.min(maxLength, Math.min(common1.length(), common2.length()) );
for (int i=0; i<n; i++) {
if (common1.charAt(i)!=common2.charAt(i)) return i;
}
return n; // first n characters are the same
}
public StringWrapper prepare(String s) { return innerDistance.prepare(s); }
}
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