Add filterKeys() method to KeyCollection

src/KeyCollection.php

@@ -95,6 +95,17 @@ public function diff($keys)
         return $this->fresh(array_diff($this->keys, ($keys instanceof self) ? $keys->keys() : (array)$keys));
     }
 
+    /**
+     * Filter the keys in the collection using a callback.
+     *
+     * @param callable $callback
+     * @return KeyCollection
+     */
+    public function filterKeys(callable $callback)
+    {
+        return $this->fresh(array_values(array_filter($this->keys, $callback)));
+    }
+
     /**
      * Read only the first key.
      *

tests/KeyCollectionTest.php

@@ -190,4 +190,15 @@ public function testPluckMethodWithKey()
         $this->assertEquals('Test 1', $list[3]);
         $this->assertEquals('Test 2', $list[4]);
     }
+
+    public function testFilterKeys()
+    {
+        $model = Mockery::mock(Model::class);
+        $collection = new KeyCollection($model, [1, 2, 3, 4]);
+        $filtered = $collection->filterKeys(function ($key) {
+            return $key % 2 == 0;
+        });
+        $this->assertInstanceOf(KeyCollection::class, $filtered);
+        $this->assertEquals([2, 4], $filtered->keys());
+    }
 }