Short syntax for applied operations

src/Phpml/FeatureExtraction/TfIdfTransformer.php

@@ -43,15 +43,13 @@ public function transform(array &$samples)
     {
         foreach ($samples as &$sample) {
             foreach ($sample as $index => &$feature) {
-                $feature = $feature * $this->idf[$index];
+                $feature *= $this->idf[$index];
             }
         }
     }
 
     /**
      * @param array $samples
-     *
-     * @return array
      */
     private function countTokensFrequency(array $samples)
     {

src/Phpml/FeatureExtraction/TokenCountVectorizer.php

@@ -173,8 +173,6 @@ private function updateFrequency(string $token)
 
     /**
      * @param array $samples
-     *
-     * @return array
      */
     private function checkDocumentFrequency(array &$samples)
     {

src/Phpml/Math/Statistic/Correlation.php

@@ -33,9 +33,9 @@ public static function pearson(array $x, array $y)
         for ($i = 0; $i < $count; ++$i) {
             $a = $x[$i] - $meanX;
             $b = $y[$i] - $meanY;
-            $axb = $axb + ($a * $b);
-            $a2 = $a2 + pow($a, 2);
-            $b2 = $b2 + pow($b, 2);
+            $axb += ($a * $b);
+            $a2 += pow($a, 2);
+            $b2 += pow($b, 2);
         }
 
         $corr = $axb / sqrt((float) ($a2 * $b2));

src/Phpml/Metric/Accuracy.php

@@ -31,7 +31,7 @@ public static function score(array $actualLabels, array $predictedLabels, bool $
         }
 
         if ($normalize) {
-            $score = $score / count($actualLabels);
+            $score /= count($actualLabels);
         }
 
         return $score;

src/Phpml/Preprocessing/Normalizer.php

@@ -64,7 +64,7 @@ private function normalizeL1(array &$sample)
             $sample = array_fill(0, $count, 1.0 / $count);
         } else {
             foreach ($sample as &$feature) {
-                $feature = $feature / $norm1;
+                $feature /= $norm1;
             }
         }
     }
@@ -84,7 +84,7 @@ private function normalizeL2(array &$sample)
             $sample = array_fill(0, count($sample), 1);
         } else {
             foreach ($sample as &$feature) {
-                $feature = $feature / $norm2;
+                $feature /= $norm2;
             }
         }
     }