Question

_______ groups documents by some specified expression and outputs to the next stage a document for each distinct grouping.

(a) $setcon

(b) $group

(c) $match

(d) None of the mentioned

This question was addressed to me in a national level competition.

Origin of the question is SQL to Aggregation Mapping Chart in section Aggregation Concepts and Aggregation Mechanics of MongoDB

Answer 1

Correct answer is (b) $group

For explanation I would say: $group works similar to group by clause in SQL.