Mongos aggregation execution error

  mongodb, question

I want to use mongo’s aggregation to calculate uv, but the following command, as shown in figure:
Error reported, aggregationresultsexceeds maximumdocumentsize (16mb)

The document mentions this problem as shown in the figure.,

Please help me see

There is too much data to process. You can use $project to select the next field and then group.

 xxx : 1,
 yyy : 1,
 }  ...