withFilter instead of filter

by

From the Scala docs:

Note: the difference between c filter p and c withFilter p is that the former
creates a new collection, whereas the latter only restricts the domain of
subsequent map, flatMap, foreach, and withFilter operations.

So filter will take the original collection and produce a new collection, but withFilter will non-strictly (i.e. lazily) pass unfiltered values through to later map/flatMap/withFilter calls, saving a second pass through the (filtered) collection. Hence it will be more efficient when passing through to these subsequent method calls.

In fact, withFilter is specifically designed for working with chains of these methods, which is what a for comprehension is de-sugared into. No other methods (such as forall/exists) are required for this, so they have not been added to the FilterMonadic return type of withFilter.

More Related Contents:

  1. Scala 2.8 breakOut
  2. Is the Scala 2.8 collections library a case of “the longest suicide note in history”? [closed]
  3. Why is Scala’s immutable Set not covariant in its type?
  4. What is the difference between JavaConverters and JavaConversions in Scala?
  5. Method parameters validation in Scala, with for comprehension and monads
  6. Composing Option with List in for-comprehension gives type mismatch depending on order
  7. Confused with the for-comprehension to flatMap/Map transformation
  8. Getting the desugared part of a Scala for/comprehension expression?
  9. When should I choose Vector in Scala?
  10. What does param: _* mean in Scala?
  11. Cartesian product of two lists
  12. Scala 2.8 collections design tutorial
  13. What type to use to store an in-memory mutable data table in Scala?
  14. Scala Map implementation keeping entries in insertion order?
  15. Stream vs Views vs Iterators
  16. How to read files from resources folder in Scala?
  17. Function returns an empty List in Spark
  18. Forward References – why does this code compile?
  19. Scala: Why does Seq.contains take an Any argument, instead of an argument of the sequence type?
  20. What does a lazy val do?
  21. Scala “
  22. Reduce, fold or scan (Left/Right)?
  23. `def` vs `val` vs `lazy val` evaluation in Scala
  24. Scala Sets contain the same elements, but sameElements() returns false
  25. Difference between MutableList and ListBuffer
  26. Scala: Parallel collection in object initializer causes a program to hang
  27. Scala best way of turning a Collection into a Map-by-key?
  28. scala parallel collections degree of parallelism
  29. Debugging Scala code with simple-build-tool (sbt) and IntelliJ
  30. Scala asInstanceOf with parameterized types

Leave a Comment