[TEXT-158] Incorrect values for Jaccard similarity with empty strings

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 1.6, 1.9
• Fix Version/s: 1.10.0
• Assignee: Bruno P. Kinoshita
• Reporter: Bruno P. Kinoshita
• Created: 09/Mar/19 10:13
• Updated: 31/Jul/20 00:24
• Resolved: 31/Jul/20 00:24

Description

In a discussion part of TEXT-126, it was pointed that the Jaccard similarity returns 0.0, and the distance 1.0. While in other libraries it returns the opposite for each.

package br.eti.kinoshita.tests.text;

import java.util.Collections;

public class EditDistances {

    public static void main(String[] args) {
        System.out.println("Testing jaccard sim/dis with empty strings");
        System.out.println("---");
        org.simmetrics.metrics.Jaccard<String> j1 = new org.simmetrics.metrics.Jaccard<>();
        float s1 = j1.compare(Collections.emptySet(), Collections.emptySet());
        System.out.println("Simmetrics Jaccard similarity: " + s1);
        float d1 = j1.distance(Collections.emptySet(), Collections.emptySet());
        System.out.println("Simmetrics Jaccard distance: " + d1);
        
        System.out.println("---");
        
        info.debatty.java.stringsimilarity.Jaccard j2 = new info.debatty.java.stringsimilarity.Jaccard();
        double s2 = j2.similarity("", "");
        System.out.println("javastringsimilarity Jaccard similarity: " + s2);
        double d2 = j2.distance("", "");
        System.out.println("javastringsimilarity Jaccard distance: " + d2);
        
        System.out.println("---");
        
        org.apache.commons.text.similarity.JaccardSimilarity j3_1 = new org.apache.commons.text.similarity.JaccardSimilarity();
        double s3 = j3_1.apply("", "");
        System.out.println("commons-text Jaccard similarity: " + s3);
        org.apache.commons.text.similarity.JaccardDistance j3_2 = new org.apache.commons.text.similarity.JaccardDistance();
        double d3 = j3_2.apply("", "");
        System.out.println("commons-text Jaccard distance: " + d3);
    }
}

Produces:

Testing jaccard sim/dis with empty strings
---
Simmetrics Jaccard similarity: 1.0
Simmetrics Jaccard distance: 0.0
---
javastringsimilarity Jaccard similarity: 1.0
javastringsimilarity Jaccard distance: 0.0
---
commons-text Jaccard similarity: 0.0
commons-text Jaccard distance: 1.0

We need to confirm what's the correct output for similarity and distance with empty strings. And either document why we are returning what we are returning, or fix it as a bug for the next release.

Issue Links

• is related to: TEXT-126 Dice's Coefficient Algorithm in String similarity
• links to: GitHub Pull Request #112