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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Work logged] (TEXT-126) Dice's Coefficient Algorithm in String similarity
Date Sat, 02 Mar 2019 20:38:00 GMT

     [ https://issues.apache.org/jira/browse/TEXT-126?focusedWorklogId=206786&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-206786
]

ASF GitHub Bot logged work on TEXT-126:
---------------------------------------

                Author: ASF GitHub Bot
            Created on: 02/Mar/19 20:37
            Start Date: 02/Mar/19 20:37
    Worklog Time Spent: 10m 
      Work Description: aherbert commented on pull request #103: TEXT-126: Adding Sorensen-Dice
similarity algoritham
URL: https://github.com/apache/commons-text/pull/103#discussion_r261841223
 
 

 ##########
 File path: src/main/java/org/apache/commons/text/similarity/SorensenDicesSimilarity.java
 ##########
 @@ -0,0 +1,74 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.text.similarity;
+
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ *
+ * @since 1.7
+ */
+public class SorensenDicesSimilarity implements SimilarityScore<Double> {
+
+    /**
+     * @param left  the first CharSequence, must not be null
+     * @param right the second CharSequence, must not be null
+     * @return result similarity
+     * @throws IllegalArgumentException if either CharSequence input is {@code null}
+     */
+
+    @Override
+    public Double apply(final CharSequence left, final CharSequence right) {
+
+        if (left == null || right == null) {
+            throw new IllegalArgumentException("CharSequences must not be null");
+        }
+
+        if (left.equals(right)) {
+            return 1d;
+        }
+
+        if ("".equals(left) || "".equals(right)) {
 
 Review comment:
   The line above the length comparison has an attempt at testing for equality:
   
   ```
   if (left.equals(right)) {
       return 1d;
   }
   ```
   
   So the code will not reach the length check anyway. 
   
   However I note that the use of `equals` is actually invalid. It is not defined in the `CharSequence`
interface and so comparing a `String` with a `StringBuilder` would fail even if they have
the same chars because `String.equals` only matches other `String` objects.
   
   Note also that this is an algorithm that does comparisons using at least two characters.
So inputting a single character is not valid for the main algorithm processing. It needs to
be handled as an edge case.
   
   So handling char sequences of a single character should return 1 or 0 (because there are
no bigrams). It makes more sense to return 1. The decision needs to be in the Javadoc. I would
vote for returning 1.
   
   Here are the edge cases and proposed results:
   
   ```
   null   vs null         IllegalArgumentException
   ""     vs ""           1
   "a"    vs "a"          1
   "ab"   vs "ab"         1
   "abc"  vs "abd"        0.5   { [ab][bc]   verses   [ab][bd] = 2 * 1 / (2 + 2) }
   ```
   
   
   
   So you need something like:
   
   ```
   if (left == null || right == null) {
       throw new IllegalArgumentException("CharSequences must not be null");
   }
   
   // Edge case for equality. Use Commons-Lang StringUtils which is a project dependency.
   if (StringUtils.equals(left, right)) {
       return 1d;
   }
   
   // Edge case for input not analysed by the algorithm
   if (left.length() <= 2 || right.length() <= 2) {
       // No bigrams
       return 0d;
   }
   ```
 
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Issue Time Tracking
-------------------

    Worklog Id:     (was: 206786)
    Time Spent: 5h  (was: 4h 50m)

> Dice's Coefficient Algorithm in String similarity
> -------------------------------------------------
>
>                 Key: TEXT-126
>                 URL: https://issues.apache.org/jira/browse/TEXT-126
>             Project: Commons Text
>          Issue Type: Improvement
>            Reporter: Vicky Chawda
>            Priority: Major
>          Time Spent: 5h
>  Remaining Estimate: 0h
>
> I'd like to propose an extension to the algorithms for string similarity in *commons-text/src/main/java/org/apache/commons/text/similarity/*
>  Dice's Coefficient Algorithm can be helpful for many who are looking for ranking similarities
in strings.
> *Inspired from* - [http://www.catalysoft.com/articles/StrikeAMatch.html]



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