From ff118eb2ba157c804919686a0a833179d0a0d0d6 Mon Sep 17 00:00:00 2001
From: Arkadiusz Kondas <arkadiusz.kondas@gmail.com>
Date: Mon, 13 May 2019 22:10:34 +0200
Subject: [PATCH] Implement LambdaTransformer (#381)

---
 src/Preprocessing/LambdaTransformer.php       | 30 +++++++++++++++++++
 tests/Preprocessing/LambdaTransformerTest.php | 28 +++++++++++++++++
 2 files changed, 58 insertions(+)
 create mode 100644 src/Preprocessing/LambdaTransformer.php
 create mode 100644 tests/Preprocessing/LambdaTransformerTest.php

diff --git a/src/Preprocessing/LambdaTransformer.php b/src/Preprocessing/LambdaTransformer.php
new file mode 100644
index 0000000..f6b5a8b
--- /dev/null
+++ b/src/Preprocessing/LambdaTransformer.php
@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Phpml\Preprocessing;
+
+final class LambdaTransformer implements Preprocessor
+{
+    /**
+     * @var callable
+     */
+    private $lambda;
+
+    public function __construct(callable $lambda)
+    {
+        $this->lambda = $lambda;
+    }
+
+    public function fit(array $samples, ?array $targets = null): void
+    {
+        // nothing to do
+    }
+
+    public function transform(array &$samples, ?array &$targets = null): void
+    {
+        foreach ($samples as &$sample) {
+            $sample = call_user_func($this->lambda, $sample);
+        }
+    }
+}
diff --git a/tests/Preprocessing/LambdaTransformerTest.php b/tests/Preprocessing/LambdaTransformerTest.php
new file mode 100644
index 0000000..6f46f3e
--- /dev/null
+++ b/tests/Preprocessing/LambdaTransformerTest.php
@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Phpml\Tests\Preprocessing;
+
+use Phpml\Preprocessing\LambdaTransformer;
+use PHPUnit\Framework\TestCase;
+
+final class LambdaTransformerTest extends TestCase
+{
+    public function testLambdaSampleTransformation(): void
+    {
+        $transformer = new LambdaTransformer(static function ($sample): int {
+            return $sample[0] + $sample[1];
+        });
+
+        $samples = [
+            [1, 2],
+            [3, 4],
+            [5, 6],
+        ];
+
+        $transformer->transform($samples);
+
+        self::assertEquals([3, 7, 11], $samples);
+    }
+}