MongoDB 4 Quick Start Guide

Aggregation pipeline expression operators

The following table summarizes the key aggregation pipeline operators (https://docs.mongodb.com/manual/meta/aggregation-quick-reference/#operator-expressions) that are currently available:

Arithmetic	This set currently consists of 15 basic operators, which let you perform arithmetic operations including $add, $subtract, $multiply, and so on.
Array	These operators are needed when a document contains an array property. Notable operators in this set include: $in: Used to determine if a value is in an array or not $size: Gives you the number of elements in the array $slice: Returns a subset of the array
Boolean	Used to formulate complex conditions. These include $and, $or, and $not.
Comparison ...