[8.x] Add reduce with keys to collections and lazy collections (#35839)

* add reduce with keys to collections

* add reduce with keys to lazy collections

* add test for reduce with keys

* fix style

src/Illuminate/Collections/Collection.php

@@ -884,6 +884,24 @@ public function reduce(callable $callback, $initial = null)
         return array_reduce($this->items, $callback, $initial);
     }
 
+    /**
+     * Reduce an associative collection to a single value.
+     *
+     * @param  callable  $callback
+     * @param  mixed $initial
+     * @return mixed
+     */
+    public function reduceWithKeys(callable $callback, $initial = null)
+    {
+        $result = $initial;
+
+        foreach ($this->items as $key => $value) {
+            $result = $callback($result, $value, $key);
+        }
+
+        return $result;
+    }
+
     /**
      * Replace the collection items with the given items.
      *

src/Illuminate/Collections/LazyCollection.php

@@ -845,6 +845,24 @@ public function reduce(callable $callback, $initial = null)
         return $result;
     }
 
+    /**
+     * Reduce an associative collection to a single value.
+     *
+     * @param  callable  $callback
+     * @param  mixed $initial
+     * @return mixed
+     */
+    public function reduceWithKeys(callable $callback, $initial = null)
+    {
+        $result = $initial;
+
+        foreach ($this as $key => $value) {
+            $result = $callback($result, $value, $key);
+        }
+
+        return $result;
+    }
+
     /**
      * Replace the collection items with the given items.
      *

tests/Support/SupportCollectionTest.php

@@ -3592,6 +3592,20 @@ public function testReduce($collection)
         }));
     }
 
+    /**
+     * @dataProvider collectionClassProvider
+     */
+    public function testReduceWithKeys($collection)
+    {
+        $data = new $collection([
+            'foo' => 'bar',
+            'baz' => 'qux',
+        ]);
+        $this->assertEquals('foobarbazqux', $data->reduceWithKeys(function ($carry, $element, $key) {
+            return $carry .= $key.$element;
+        }));
+    }
+
     /**
      * @dataProvider collectionClassProvider
      */