Array subset in aggregation framework pipeline

Question

In a previous question I wanted to obtain a count of the resulting groups using pipeline operations. As suggested, I used the following:

db.test.aggregate(
          


        

Answer 1

Unfortunately there is currently (as at MongoDB 2.2) no Aggregation Framework operator to $slice or take a subset of an array.

You will need to use a workaround such as:

• your use of $skip and $limit in the aggregate() pipeline
• manipulation of the results in your application code.
• implementing the aggregation using Map/Reduce

There is an existing feature request in the MongoDB issue tracker that you can upvote/watch: SERVER-6074: Allow $slice operator in $project.