create StratifiedRandomSplit for cross validation

src/Phpml/CrossValidation/RandomSplit.php

@@ -5,101 +5,26 @@ declare (strict_types = 1);
 namespace Phpml\CrossValidation;
 
 use Phpml\Dataset\Dataset;
-use Phpml\Exception\InvalidArgumentException;
 
-class RandomSplit
+class RandomSplit extends Split
 {
-    /**
-     * @var array
-     */
-    private $trainSamples = [];
-
-    /**
-     * @var array
-     */
-    private $testSamples = [];
-
-    /**
-     * @var array
-     */
-    private $trainLabels = [];
-
-    /**
-     * @var array
-     */
-    private $testLabels = [];
-
     /**
      * @param Dataset $dataset
      * @param float   $testSize
-     * @param int     $seed
-     *
-     * @throws InvalidArgumentException
      */
-    public function __construct(Dataset $dataset, float $testSize = 0.3, int $seed = null)
+    protected function splitDataset(Dataset $dataset, float $testSize)
     {
-        if (0 >= $testSize || 1 <= $testSize) {
-            throw InvalidArgumentException::percentNotInRange('testSize');
-        }
-        $this->seedGenerator($seed);
-
         $samples = $dataset->getSamples();
         $labels = $dataset->getTargets();
         $datasetSize = count($samples);
+        $testCount = count($this->testSamples);
 
         for ($i = $datasetSize; $i > 0; --$i) {
             $key = mt_rand(0, $datasetSize - 1);
-            $setName = count($this->testSamples) / $datasetSize >= $testSize ? 'train' : 'test';
+            $setName = (count($this->testSamples) - $testCount) / $datasetSize >= $testSize ? 'train' : 'test';
 
             $this->{$setName.'Samples'}[] = $samples[$key];
             $this->{$setName.'Labels'}[] = $labels[$key];
-
-            $samples = array_values($samples);
-            $labels = array_values($labels);
-        }
-    }
-
-    /**
-     * @return array
-     */
-    public function getTrainSamples()
-    {
-        return $this->trainSamples;
-    }
-
-    /**
-     * @return array
-     */
-    public function getTestSamples()
-    {
-        return $this->testSamples;
-    }
-
-    /**
-     * @return array
-     */
-    public function getTrainLabels()
-    {
-        return $this->trainLabels;
-    }
-
-    /**
-     * @return array
-     */
-    public function getTestLabels()
-    {
-        return $this->testLabels;
-    }
-
-    /**
-     * @param int|null $seed
-     */
-    private function seedGenerator(int $seed = null)
-    {
-        if (null === $seed) {
-            mt_srand();
-        } else {
-            mt_srand($seed);
         }
     }
 }

src/Phpml/CrossValidation/Split.php

@@ -0,0 +1,94 @@
+<?php
+
+declare (strict_types = 1);
+
+namespace Phpml\CrossValidation;
+
+use Phpml\Dataset\Dataset;
+use Phpml\Exception\InvalidArgumentException;
+
+abstract class Split
+{
+    /**
+     * @var array
+     */
+    protected $trainSamples = [];
+
+    /**
+     * @var array
+     */
+    protected $testSamples = [];
+
+    /**
+     * @var array
+     */
+    protected $trainLabels = [];
+
+    /**
+     * @var array
+     */
+    protected $testLabels = [];
+
+    /**
+     * @param Dataset $dataset
+     * @param float   $testSize
+     * @param int     $seed
+     *
+     * @throws InvalidArgumentException
+     */
+    public function __construct(Dataset $dataset, float $testSize = 0.3, int $seed = null)
+    {
+        if (0 >= $testSize || 1 <= $testSize) {
+            throw InvalidArgumentException::percentNotInRange('testSize');
+        }
+        $this->seedGenerator($seed);
+
+        $this->splitDataset($dataset, $testSize);
+    }
+
+    abstract protected function splitDataset(Dataset $dataset, float $testSize);
+
+    /**
+     * @return array
+     */
+    public function getTrainSamples()
+    {
+        return $this->trainSamples;
+    }
+
+    /**
+     * @return array
+     */
+    public function getTestSamples()
+    {
+        return $this->testSamples;
+    }
+
+    /**
+     * @return array
+     */
+    public function getTrainLabels()
+    {
+        return $this->trainLabels;
+    }
+
+    /**
+     * @return array
+     */
+    public function getTestLabels()
+    {
+        return $this->testLabels;
+    }
+
+    /**
+     * @param int|null $seed
+     */
+    protected function seedGenerator(int $seed = null)
+    {
+        if (null === $seed) {
+            mt_srand();
+        } else {
+            mt_srand($seed);
+        }
+    }
+}

src/Phpml/CrossValidation/StratifiedRandomSplit.php

@@ -0,0 +1,62 @@
+<?php
+
+declare (strict_types = 1);
+
+namespace Phpml\CrossValidation;
+
+use Phpml\Dataset\ArrayDataset;
+use Phpml\Dataset\Dataset;
+
+class StratifiedRandomSplit extends RandomSplit
+{
+    /**
+     * @param Dataset $dataset
+     * @param float   $testSize
+     */
+    protected function splitDataset(Dataset $dataset, float $testSize)
+    {
+        $datasets = $this->splitByTarget($dataset);
+
+        foreach ($datasets as $targetSet) {
+            parent::splitDataset($targetSet, $testSize);
+        }
+    }
+
+    /**
+     * @param Dataset $dataset
+     *
+     * @return Dataset[]|array
+     */
+    private function splitByTarget(Dataset $dataset): array
+    {
+        $targets = $dataset->getTargets();
+        $samples = $dataset->getSamples();
+
+        $uniqueTargets = array_unique($targets);
+        $split = array_combine($uniqueTargets, array_fill(0, count($uniqueTargets), []));
+
+        foreach ($samples as $key => $sample) {
+            $split[$targets[$key]][] = $sample;
+        }
+
+        $datasets = $this->createDatasets($uniqueTargets, $split);
+
+        return $datasets;
+    }
+
+    /**
+     * @param array $uniqueTargets
+     * @param array $split
+     *
+     * @return array
+     */
+    private function createDatasets(array $uniqueTargets, array $split): array
+    {
+        $datasets = [];
+        foreach ($uniqueTargets as $target) {
+            $datasets[$target] = new ArrayDataset($split[$target], array_fill(0, count($split[$target]), $target));
+        }
+
+        return $datasets;
+    }
+}

tests/Phpml/CrossValidation/StratifiedRandomSplitTest.php

@@ -0,0 +1,65 @@
+<?php
+
+declare (strict_types = 1);
+
+namespace tests\Phpml\CrossValidation;
+
+use Phpml\CrossValidation\StratifiedRandomSplit;
+use Phpml\Dataset\ArrayDataset;
+
+class StratifiedRandomSplitTest extends \PHPUnit_Framework_TestCase
+{
+    public function testDatasetStratifiedRandomSplitWithEvenDistribution()
+    {
+        $dataset = new ArrayDataset(
+            $samples = [[1], [2], [3], [4], [5], [6], [7], [8]],
+            $labels = ['a', 'a', 'a', 'a', 'b', 'b', 'b', 'b']
+        );
+
+        $split = new StratifiedRandomSplit($dataset, 0.5);
+
+        $this->assertEquals(2, $this->countSamplesByTarget($split->getTestLabels(), 'a'));
+        $this->assertEquals(2, $this->countSamplesByTarget($split->getTestLabels(), 'b'));
+
+        $split = new StratifiedRandomSplit($dataset, 0.25);
+
+        $this->assertEquals(1, $this->countSamplesByTarget($split->getTestLabels(), 'a'));
+        $this->assertEquals(1, $this->countSamplesByTarget($split->getTestLabels(), 'b'));
+    }
+
+    public function testDatasetStratifiedRandomSplitWithEvenDistributionAndNumericTargets()
+    {
+        $dataset = new ArrayDataset(
+            $samples = [[1], [2], [3], [4], [5], [6], [7], [8]],
+            $labels = [1, 2, 1, 2, 1, 2, 1, 2]
+        );
+
+        $split = new StratifiedRandomSplit($dataset, 0.5);
+
+        $this->assertEquals(2, $this->countSamplesByTarget($split->getTestLabels(), 1));
+        $this->assertEquals(2, $this->countSamplesByTarget($split->getTestLabels(), 2));
+
+        $split = new StratifiedRandomSplit($dataset, 0.25);
+
+        $this->assertEquals(1, $this->countSamplesByTarget($split->getTestLabels(), 1));
+        $this->assertEquals(1, $this->countSamplesByTarget($split->getTestLabels(), 2));
+    }
+
+    /**
+     * @param $splitTargets
+     * @param $countTarget
+     *
+     * @return int
+     */
+    private function countSamplesByTarget($splitTargets, $countTarget): int
+    {
+        $count = 0;
+        foreach ($splitTargets as $target) {
+            if ($target === $countTarget) {
+                ++$count;
+            }
+        }
+
+        return $count;
+    }
+}