Create the Truncation Selection

src/GeneticSharp.Benchmarks/SelectionsBenchmark.cs

@@ -54,5 +54,21 @@ public ISelection Tournament()
             target.SelectChromosomes(_chromosomesNumber, _generation);
             return target;
         }
+
+        [Benchmark]
+        public ISelection Rank()
+        {
+            var target = new RankSelection();
+            target.SelectChromosomes(_chromosomesNumber, _generation);
+            return target;
+        }
+
+        [Benchmark]
+        public ISelection Truncation()
+        {
+            var target = new TruncationSelection();
+            target.SelectChromosomes(_chromosomesNumber, _generation);
+            return target;
+        }
     }
 }

src/GeneticSharp.Domain.UnitTests/Selections/TruncationSelectionTest.cs

@@ -0,0 +1,80 @@
+using System;
+using System.Collections.Generic;
+using NUnit.Framework;
+using NSubstitute;
+
+namespace GeneticSharp.Domain.UnitTests.Selections
+{
+    [TestFixture()]
+    [Category("Selections")]
+    public class TruncationSelectionTest
+    {
+        [Test()]
+        public void SelectChromosomes_InvalidNumber_Exception()
+        {
+            var target = new TruncationSelection();
+
+            Assert.Catch<ArgumentOutOfRangeException>(() =>
+            {
+                target.SelectChromosomes(-1, null);
+            }, "The number of selected chromosomes should be at least 2.");
+
+            Assert.Catch<ArgumentOutOfRangeException>(() =>
+            {
+                target.SelectChromosomes(0, null);
+            }, "The number of selected chromosomes should be at least 2.");
+
+            Assert.Catch<ArgumentOutOfRangeException>(() =>
+            {
+                target.SelectChromosomes(1, null);
+            }, "The number of selected chromosomes should be at least 2.");
+        }
+
+        [Test()]
+        public void SelectChromosomes_NullGeneration_Exception()
+        {
+            var target = new TruncationSelection();
+
+            var actual = Assert.Catch<ArgumentNullException>(() =>
+            {
+                target.SelectChromosomes(2, null);
+            });
+
+            Assert.AreEqual("generation", actual.ParamName);
+        }
+
+        [Test()]
+        public void SelectChromosomes_Generation_ChromosomesSelected()
+        {
+            var target = new TruncationSelection();
+            var c1 = Substitute.ForPartsOf<ChromosomeBase>(2);
+            c1.Fitness = 0.1;
+
+            var c2 = Substitute.ForPartsOf<ChromosomeBase>(2);
+            c2.Fitness = 0.5;
+
+            var c3 = Substitute.ForPartsOf<ChromosomeBase>(2);
+            c3.Fitness = 0;
+
+            var c4 = Substitute.ForPartsOf<ChromosomeBase>(2);
+            c4.Fitness = 0.7;
+
+            var generation = new Generation(1, new List<IChromosome>() {
+                c1, c2, c3, c4
+            });
+
+
+            var actual = target.SelectChromosomes(2, generation);
+            Assert.AreEqual(2, actual.Count);
+            Assert.AreEqual(0.7, actual[0].Fitness);
+            Assert.AreEqual(0.5, actual[1].Fitness);
+
+            actual = target.SelectChromosomes(3, generation);
+            Assert.AreEqual(3, actual.Count);
+            Assert.AreEqual(0.7, actual[0].Fitness);
+            Assert.AreEqual(0.5, actual[1].Fitness);
+            Assert.AreEqual(0.1, actual[2].Fitness);
+        }
+    }
+}
+

src/GeneticSharp.Domain/Selections/TruncationSelection.cs

@@ -0,0 +1,35 @@
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Linq;
+
+namespace GeneticSharp
+{
+    /// <summary>
+    /// Selects the chromosomes with the best fitness.
+    /// </summary>
+    /// <remarks>
+    /// <see href="https://en.wikipedia.org/wiki/Truncation_selection"/>
+    /// </remarks>
+    [DisplayName("Truncation")]
+    public sealed class TruncationSelection : SelectionBase
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="GeneticSharp.Domain.Selections.TruncationSelection"/> class.
+        /// </summary>
+        public TruncationSelection() : base(2)
+        {
+        }        
+
+        /// <summary>
+        /// Performs the selection of chromosomes from the generation specified.
+        /// </summary>
+        /// <param name="number">The number of chromosomes to select.</param>
+        /// <param name="generation">The generation where the selection will be made.</param>
+        /// <returns>The select chromosomes.</returns>
+        protected override IList<IChromosome> PerformSelectChromosomes(int number, Generation generation)
+        {
+            var ordered = generation.Chromosomes.OrderByDescending(c => c.Fitness);
+            return ordered.Take(number).ToList();
+        }        
+    }
+}