public IEnumerable IndexingFunction(IEnumerable <dynamic> items)
        {
            try
            {
                EnsureGroupItemCreated();
                foreach (DynamicBlittableJson item in items)
                {
                    if (_groupedItems.TryGetValue(item.BlittableJson, out var list) == false)
                    {
                        list = new List <BlittableJsonReaderObject>();
                        _groupedItems[item.BlittableJson] = list;
                    }
                    list.Add(item.BlittableJson);
                }
                foreach (var item in _groupedItems.Values)
                {
                    Engine.ResetCallStack();
                    Engine.ResetStatementsCount();
                    Engine.ResetTimeoutTicks();

                    _oneItemArray[0] = ConstructValues(item);
                    JsValue jsItem = null;
                    try
                    {
                        jsItem = Reduce.Call(JsValue.Null, _oneItemArray).AsObject();
                    }
                    catch (JavaScriptException jse)
                    {
                        var(message, success) = JavaScriptIndexFuncException.PrepareErrorMessageForJavaScriptIndexFuncException(ReduceString, jse);
                        if (success == false)
                        {
                            throw new JavaScriptIndexFuncException($"Failed to execute {ReduceString}", jse);
                        }
                        throw new JavaScriptIndexFuncException($"Failed to execute reduce script, {message}", jse);
                    }
                    catch (Exception e)
                    {
                        throw new JavaScriptIndexFuncException($"Failed to execute {ReduceString}", e);
                    }
                    yield return(jsItem);

                    _resolver.ExplodeArgsOn(null, null);
                }
            }
            finally
            {
                _oneItemArray[0] = null;
                _groupedItems.Clear();
            }
        }