patch

src/Mapper.php

@@ -73,6 +73,25 @@ public function toArray(): array
         return $this->resolveToArray((array) $this,  static::getRules(new \ReflectionClass(static::class)));
     }
 
+    /**
+     * Get data (filtered)
+     *
+     * @param array|string $keys
+     * @return array
+     */
+    public function only(array|string $keys): array
+    {
+        $keys = (array) $keys;
+
+        return array_filter(
+            $this->toArray(),
+            function ($key) use ($keys) {
+                return in_array($key, $keys);
+            },
+            ARRAY_FILTER_USE_KEY
+        );
+    }
+
     /**
      * @see \JsonSerializable
      *
@@ -191,7 +210,7 @@ protected static function getRules(\ReflectionClass $class): array
      * @param array $rule
      * @param \ReflectionAttribute $attribute
      * @throws \RuntimeException
-     * @return string
+     * @return array
      */
     protected static function handleAttribute(array $rule, \ReflectionAttribute $attribute): array
     {

tests/MapperTest.php

@@ -43,6 +43,9 @@ public function test_simple()
             $mapper->toArray()
         );
 
+        $this->assertSame(['a' => '1'], $mapper->only('a'));
+        $this->assertSame(['a' => '1', 'b' => null], $mapper->only(['a', 'b']));
+
         $this->assertSame(
             json_encode([
                 'a' => '1',