document reduce many

Author: taylorotwell

collections.md

@@ -164,6 +164,7 @@ For the majority of the remaining collection documentation, we'll discuss each m
 [put](#method-put)
 [random](#method-random)
 [reduce](#method-reduce)
+[reduceMany](#method-reduce-many)
 [reject](#method-reject)
 [replace](#method-replace)
 [replaceRecursive](#method-replacerecursive)
@@ -1725,6 +1726,25 @@ The `reduce` method also passes array keys in associative collections to the giv
 
     // 4264
 
+<a name="method-reduce-many"></a>
+#### `reduceMany()` {#collection-method}
+
+The `reduceMany` method reduces the collection to an array of values, passing the results of each iteration into the subsequent iteration. This method is similar to the `reduce` method; however, it can accept multiple initial values:
+
+```php
+[$creditsRemaining, $batch] = Image::where('status', 'unprocessed')
+        ->get()
+        ->reduceMany(function ($creditsRemaining, $batch, $image) {
+            if ($creditsRemaining >= $image->creditsRequired()) {
+                $batch->push($image);
+
+                $creditsRemaining -= $image->creditsRequired();
+            }
+
+            return [$creditsRemaining, $batch];
+        }, $creditsAvailable, collect());
+```
+
 <a name="method-reject"></a>
 #### `reject()` {#collection-method}