Pivoting array items by a key

In some scenarios, an array field within documents contains a sequence of elements where some of the array's elements logically relate to each other. In this example, you will explore how to construct a pipeline that restructures arrays to represent these inherent groupings.

Scenario

You have a set of geographically dispersed weather station zones where each zone has multiple sensor devices collecting readings such as temperature, humidity, and pressure. Each weather station assembles readings from its devices and once per hour transmits this set of measurements to a central database to store. The set of persisted readings is randomly ordered measurements for different devices in the zone. You need to take the mix of readings and group them by device, so the weather data is easier to consume by downstream dashboards and applications.

Note

This example's pipeline relies on some of the more difficult-to-understand array operator expressions...