Implement simple crossover

Author: petercoles

src/Population.php

@@ -41,6 +41,26 @@ public function select($number)
         return collect($this->solutions)->sortByDesc('fitness')->take($number);
     }
 
+    public function crossover($parents)
+    {
+        $numParents = $parents->count();
+        $familySize = 2 * $this->size / $numParents;
+        $chromosomeCount = sizeof($parents->first()->chromosomes());
+
+        if (is_int($familySize)) {
+            $this->solutions = $parents->shuffle()->chunk(2)->map(function ($parents) use ($familySize, $chromosomeCount) {
+                $children = [];
+                for ($i = 0; $i < $familySize; $i++) {
+                    $crossover = mt_rand(0, $chromosomeCount);
+                    $left = array_slice($parents->first()->chromosomes(), 0, $crossover);
+                    $right = array_slice($parents->last()->chromosomes(), $crossover);
+                    $children[] = new $this->model(['chromosomes' => array_merge($left, $right)]);
+                }
+                return $children;
+            })->flatten();
+        }
+    }
+
     public function mutate()
     {
         $this->solutions = collect($this->solutions)->map(function ($solution) {

src/Solution.php

@@ -12,6 +12,15 @@ abstract public function genome();
 
     abstract public function evaluate($data);
 
+    public function __construct($params = null)
+    {
+        if ($params) {
+            foreach ($params as $key => $value) {
+                $this->$key = $value;
+            }
+        }
+    }
+
     public function initialise()
     {
         $this->chromosomes = collect($this->genome())->map(function ($definition) {

tests/PopulationTest.php

@@ -64,6 +64,18 @@ public function apply_selection_strategy()
         $this->assertEquals([1052, 771, 758, 683, 641, 607], $selections->pluck('fitness')->toArray());
     }
 
+    /** @test */
+    public function apply_crossover_strategy()
+    {
+        $population = new Population(Integers::class, 12);
+        $selections = collect($population->solutions())->take(6);
+        $this->assertEquals([64, -39, 1], $population->solutions()[0]->chromosomes());
+
+        $population->crossover($selections);
+        $this->assertEquals([82, -93, 0], $population->solutions()[0]->chromosomes());
+        $this->assertEquals([82, -39, 1], $population->solutions()[2]->chromosomes());
+    }
+
     /** @test */
     public function apply_mutation_strategy()
     {