https://beam.incubator.apache.org/documentation/transforms/java/aggregation/groupbykey/
GroupByKey
Apache Beam is an open source, unified model and set of language-specific SDKs for defining and executing data processing workflows, and also data ingestion...
https://beam.apache.org/releases/javadoc/2.12.0/org/apache/beam/sdk/transforms/GroupByKey.html
GroupByKey (Apache Beam 2.12.0)
apache beam