您正在正确进行聚合，但是如错误消息所示，完整的

You're doing the aggregation correctly, but as the error message indicates, the full result of the aggregate call cannot be larger than 16 MB.

解决方法是添加一个过滤器以减小结果的大小，或者改用map-reduce并将结果输出到另一个集合.

Work-arounds would be to either add a filter to reduce the size of the result or use map-reduce instead and output the result to another collection.