$group

An aggregation pipeline stage that groups documents by a specified expression and applies accumulator operators.

Syntax

mongodb

{ $group: { _id: expression, field: { $accumulator: expr } } }

Example

mongodb

db.sales.aggregate([
  { $group: {
    _id: "$category",
    total: { $sum: "$price" },
    avg: { $avg: "$price" },
    count: { $sum: 1 },
    items: { $push: "$name" }
  }}
])