mapValues
mapValues is an operation that transforms values associated with keys while preserving those keys.
Kafka Streams in Action, Second Edition
KStream.mapValues is a Kafka Streams operation that maps each record value to a new value while retaining the record key.
- How it is used
- Transforms incoming record values as a processing node between a KStream source and downstream operations.
- How deep it goes
- Defines mapper interfaces, key-preservation behavior, and topology placement, while deferring lambda-expression instruction to external documentation.
- Examples
- Demonstrates uppercasing text, masking RetailPurchase credit-card numbers, and converting proximity readings from feet to meters.
- What you can do after
- Apply it via Kafka Streams to transform each record value while retaining its existing key.
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Apache Kafka in Action
mapValues is a stream-processing function that transforms record values while preserving their keys.
- How it is used
- Transforms stream values for conversion, masking, and reshaping while preserving record keys.
- How deep it goes
- Defines value-only transformation, demonstrates price conversion, and explains repartitioning consequences without detailing processor internals.
- Examples
- Demonstrates converting prices from dollars to cents and projecting averages from aggregate state.
- What you can do after
- Apply via Kafka Streams to transform values without changing keys or unnecessarily causing repartitioning.
Related concepts
- processing nodeproduces · A processing node is a stream-processing component in a topology that processes records using logic such as filtering, aggregation, or transformation.
- mapalternative to · An operation that applies a function to values in a collection or computational context, producing corresponding results while preserving the collection or context’s structure.
- Mapuses · A map is an associative data structure that stores key-value pairs and supports retrieving values by key.
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