fix Pipeline transformation

src/Phpml/Pipeline.php

@@ -68,7 +68,7 @@ public function getEstimator()
     public function train(array $samples, array $targets)
     {
         foreach ($this->transformers as $transformer) {
-            $samples = $transformer->transform($samples);
+            $transformer->transform($samples);
         }
 
         $this->estimator->train($samples, $targets);

tests/Phpml/PipelineTest.php

@@ -7,6 +7,9 @@
 use Phpml\Classification\SVC;
 use Phpml\FeatureExtraction\TfIdfTransformer;
 use Phpml\Pipeline;
+use Phpml\Preprocessing\Imputer;
+use Phpml\Preprocessing\Normalizer;
+use Phpml\Preprocessing\Imputer\Strategy\MostFrequentStrategy;
 
 class PipelineTest extends \PHPUnit_Framework_TestCase
 {
@@ -22,4 +25,33 @@ public function testPipelineConstruction()
         $this->assertEquals($transformers, $pipeline->getTransformers());
         $this->assertEquals($estimator, $pipeline->getEstimator());
     }
+
+    public function testPipelineWorkflow()
+    {
+        $transformers = [
+            new Imputer(null, new MostFrequentStrategy()),
+            new Normalizer(),
+        ];
+        $estimator = new SVC();
+
+        $samples = [
+            [1, -1, 2],
+            [2, 0, null],
+            [null, 1, -1],
+        ];
+
+        $targets = [
+            4,
+            1,
+            4
+        ];
+
+        $pipeline = new Pipeline($transformers, $estimator);
+        $pipeline->train($samples, $targets);
+
+        $predicted = $pipeline->predict([[0, 0, 0]]);
+
+        $this->assertEquals(4, $predicted[0]);
+    }
+
 }