implemented Euclidean Distance similarity score

Recommender.Tests/EuclideanDistanceTests.cs

@@ -0,0 +1,44 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using NUnit.Framework;
+using Recommender.Data;
+
+namespace Recommender.Tests
+{
+    [TestFixture]
+    class EuclideanDistanceTests
+    {
+        private EuclideanDistance euclideanDistance;
+
+        [SetUp]
+        public void SetUp()
+        {
+            euclideanDistance = new EuclideanDistance(ReviewerBuilder.BuildReviewer1(), ReviewerBuilder.BuildReviewer2());
+        }
+
+        [Test]
+        public void TwoReviewersWithSomeSimilarReviewsShouldHaveAScoreBetweenZeroAndOne()
+        {
+            Assert.AreEqual(0.148, euclideanDistance.Score());
+        }
+
+        [Test]
+        public void ReviewersThatHaveReviewedUniqueTitlesShouldNotBeSimilar()
+        {
+            var r1 = ReviewerBuilder.BuildReviewer1();
+            var r2 = ReviewerBuilder.BuildAReviewerThatReviewedSomethingUnique();
+            euclideanDistance = new EuclideanDistance(r1, r2);
+            Assert.AreEqual(0, euclideanDistance.Score());
+        }
+
+        [Test]
+        public void ReviewersThatHaveTheSameTasteShouldHaveAPerfectScore()
+        {
+            var r1 = ReviewerBuilder.BuildReviewer1();
+            euclideanDistance = new EuclideanDistance(r1, r1);
+            Assert.AreEqual(1.0, euclideanDistance.Score());
+        }
+    }
+}

Recommender.Tests/Recommender.Tests.csproj

@@ -47,6 +47,7 @@
     <Reference Include="System.Data" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="EuclideanDistanceTests.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="Reviews\ReviewerTests.cs" />
     <Compile Include="Steps\SumDifferenceSquaresTests.cs" />

Recommender.Tests/Reviews/ReviewerTests.cs

@@ -47,15 +47,15 @@ public void TwoSimilarReviewersShouldHaveOneLikeReview()
         {
             var r1 = ReviewerBuilder.BuildOneReviewMax();
             var r2 = ReviewerBuilder.BuildOneReviewMin();
-            Assert.AreEqual(1, r1.SimilarItems(r2.Reviews).Count);
+            Assert.AreEqual(1, r1.SimilarReviews(r2.Reviews).Count);
         }
 
         [Test]
         public void ReviewersThatHaveTheSameTasteShouldHaveAllSimilarItems()
         {
             var r1 = ReviewerBuilder.BuildReviewer1();
             var r2 = ReviewerBuilder.BuildReviewer1();
-            Assert.AreEqual(6, r1.SimilarItems(r2.Reviews).Count);
+            Assert.AreEqual(6, r1.SimilarReviews(r2.Reviews).Count);
         }
     }
 }

Recommender/EuclideanDistance.cs

@@ -0,0 +1,34 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Recommender.Reviews;
+using Recommender.Steps;
+
+namespace Recommender
+{
+    public class EuclideanDistance : SimilarityScore
+    {
+        private readonly Reviewer R1;
+        private readonly Reviewer R2;
+
+        public EuclideanDistance(Reviewer r1, Reviewer r2)
+        {
+            R1 = r1;
+            R2 = r2;
+        }
+
+        public double Score()
+        {
+            var similarReviews = R1.SimilarReviews(R2.Reviews);
+
+            if (similarReviews.Count == 0)
+            {
+                return 0.0;
+            }
+
+            var sumDifferenceSquares = new SumDifferenceSquares(similarReviews, R1.Reviews, R2.Reviews).Calculate();
+            return Math.Round(1 / (1 + sumDifferenceSquares), 3);
+        }
+    }
+}

Recommender/Recommender.csproj

@@ -44,7 +44,9 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="Data\ReviewerBuilder.cs" />
+    <Compile Include="EuclideanDistance.cs" />
     <Compile Include="Reviews\Reviewer.cs" />
+    <Compile Include="SimilarityScore.cs" />
     <Compile Include="SimilarityScoreRunner.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="Steps\SimilarityScoreCommand.cs" />

Recommender/Reviews/Reviewer.cs

@@ -20,7 +20,7 @@ public void AddReview(string title, double score)
             Reviews.Add(title, score);
         }
 
-        public List<string> SimilarItems(Dictionary<string, double> compareTo)
+        public List<string> SimilarReviews(Dictionary<string, double> compareTo)
         {
             return (from r in Reviews where compareTo.ContainsKey(r.Key) select r.Key).ToList();
         }

Recommender/SimilarityScore.cs

@@ -0,0 +1,12 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace Recommender
+{
+    interface SimilarityScore
+    {
+        double Score();
+    }
+}