Add 'filter by attribute' functionality (#21898)

Author: jerguslejko

src/Illuminate/Support/Collection.php

@@ -408,11 +408,15 @@ public function except($keys)
     /**
      * Run a filter over each of the items.
      *
-     * @param  callable|null  $callback
+     * @param  mixed|null  $callback
      * @return static
      */
-    public function filter(callable $callback = null)
+    public function filter($callback = null)
     {
+        if (is_string($callback)) {
+            $callback = $this->valueRetriever($callback);
+        }
+
         if ($callback) {
             return new static(Arr::where($this->items, $callback));
         }

tests/Support/SupportCollectionTest.php

@@ -305,6 +305,13 @@ public function testFilter()
         $this->assertEquals(['first' => 'Hello', 'second' => 'World'], $c->filter(function ($item, $key) {
             return $key != 'id';
         })->all());
+
+        $c = new Collection([
+            ['value' => 'foo', 'nested' => ['included' => true]],
+            ['value' => 'bar', 'nested' => ['included' => false]],
+            ['value' => 'baz', 'nested' => ['included' => true]],
+        ]);
+        $this->assertEquals(['foo', 'baz'], $c->filter('nested.included')->pluck('value')->toArray());
     }
 
     public function testHigherOrderKeyBy()