Distance: fix bug in Hamming distance that skipped the head pair #220

src/Numerics/Distance.cs

@@ -351,7 +351,7 @@ namespace MathNet.Numerics
         {
             if (a.Length != b.Length) throw new ArgumentOutOfRangeException("b");
             int count = 0;
-            for (int i = 1; i < a.Length; i++)
+            for (int i = 0; i < a.Length; i++)
             {
                 if (a[i] != b[i])
                 {
@@ -368,7 +368,7 @@ namespace MathNet.Numerics
         {
             if (a.Length != b.Length) throw new ArgumentOutOfRangeException("b");
             int count = 0;
-            for (int i = 1; i < a.Length; i++)
+            for (int i = 0; i < a.Length; i++)
             {
                 if (a[i] != b[i])
                 {

src/UnitTests/DistanceTests.cs

@@ -0,0 +1,19 @@
+using NUnit.Framework;
+
+namespace MathNet.Numerics.UnitTests
+{
+    [TestFixture]
+    public class DistanceTests
+    {
+        [Test]
+        public void Hamming()
+        {
+            Assert.That(Distance.Hamming(new[] { 0.0, 0.0 }, new[] { 0.0, 0.0 }), Is.EqualTo(0.0));
+            Assert.That(Distance.Hamming(new[] { 1.0, 0.0 }, new[] { 1.0, 0.0 }), Is.EqualTo(0.0));
+            Assert.That(Distance.Hamming(new[] { 0.0, 0.0 }, new[] { 1.0, 0.0 }), Is.EqualTo(1.0));
+            Assert.That(Distance.Hamming(new[] { 0.0, 0.0 }, new[] { 0.0, 1.0 }), Is.EqualTo(1.0));
+            Assert.That(Distance.Hamming(new[] { 0.0, 0.0 }, new[] { 1.0, 1.0 }), Is.EqualTo(2.0));
+            Assert.That(Distance.Hamming(new[] { 1.0, 0.0 }, new[] { 0.0, 1.0 }), Is.EqualTo(2.0));
+        }
+    }
+}

src/UnitTests/UnitTests.csproj

@@ -85,6 +85,7 @@
     <Compile Include="ComplexTests\Complex32Test.TextHandling.cs" />
     <Compile Include="ComplexTests\ComplexTest.cs" />
     <Compile Include="ComplexTests\ComplexTest.TextHandling.cs" />
+    <Compile Include="DistanceTests.cs" />
     <Compile Include="DistributionTests\CommonDistributionTests.cs" />
     <Compile Include="DistributionTests\Continuous\BetaTests.cs" />
     <Compile Include="DistributionTests\Continuous\CauchyTests.cs" />