Scala: Why mapValues produces a view and is there any stable alternatives?

by

There’s a ticket about this, SI-4776 (by YT).

The commit that introduces it has this to say:

Following a suggestion of jrudolph, made filterKeys and mapValues
transform abstract maps, and duplicated functionality for immutable
maps. Moved transform and filterNot from immutable to general maps.
Review by phaller.

I have not been able to find the original suggestion by jrudolph, but I assume it was done to make mapValues more efficient. Give the question, that may come as a surprise, but mapValues is more efficient if you are not likely to iterate over the values more than once.

As a work-around, one can do mapValues(...).view.force to produce a new Map.

More Related Contents:

  1. Best way to merge two maps and sum the values of same key?
  2. Confused with the for-comprehension to flatMap/Map transformation
  3. Scala: Merge map
  4. Functional programming, Scala map and fold left [closed]
  5. How to define “type disjunction” (union types)?
  6. Spark – load CSV file as DataFrame?
  7. What is a higher kinded type in Scala?
  8. How to define partitioning of DataFrame?
  9. In Scala, what is an “early initializer”?
  10. Case class equality in Apache Spark
  11. What is the difference between Scala’s case class and class?
  12. What is the motivation for Scala assignment evaluating to Unit rather than the value assigned?
  13. Dropping a nested column from Spark DataFrame
  14. How to read records in JSON format from Kafka using Structured Streaming?
  15. What’s the difference between multiple parameters lists and multiple parameters per list in Scala?
  16. Dynamic mixin in Scala – is it possible?
  17. What’s the difference between == and .equals in Scala?
  18. Reading DataFrame from partitioned parquet file
  19. Scala: convert map to case class
  20. Build.scala, % and %% symbols meaning
  21. Can I get a compile-time list of all of the case objects which derive from a sealed parent in Scala?
  22. How are Scala traits compiled into Java bytecode?
  23. Why are singleton objects more object-oriented?
  24. In Scala, what does “view” do?
  25. How to explode an array into multiple columns in Spark
  26. How to use IntelliJ with Play Framework and Scala
  27. Spark column string replace when present in other column (row)
  28. scala f-bounded types explanation
  29. Scala variable argument list with call-by-name possible?
  30. Scalaz Bind[Seq] typeclass

Leave a Comment