CODEWITHSUNDEEP
scala
Kevin Meredith
Kevin Meredith

Reputation: 41909

Applying Multiple Filters on List

Given these two functions:

scala> def maybe(x: Int): Boolean = x % 2 == 0
maybe: (x: Int)Boolean

scala> def good(x: Int): Boolean = x == 10
good: (x: Int)Boolean

Can I apply both good and maybe functions together?

scala> List(10) filter good filter maybe
res104: List[Int] = List(10)

scala> List(10) filter (good && maybe)
<console>:17: error: missing arguments for method good;
follow this method with `_' if you want to treat it as a partially applied function
              List(10) filter (good && maybe)
                               ^

Upvotes: 1

Views: 2654

Answers (2)

som-snytt
som-snytt

Reputation: 39577

scala> def maybe(x: Int): Boolean = x % 2 == 0
maybe: (x: Int)Boolean

scala> def good(x: Int): Boolean = x % 3 == 0
good: (x: Int)Boolean

scala> (1 to 20) filter { i => List(good _, maybe _).forall(_(i)) }
res1: scala.collection.immutable.IndexedSeq[Int] = Vector(6, 12, 18)

Upvotes: 3

hsun324
hsun324

Reputation: 549

You could evaluate them inside an anonymous function:

List(10) filter { x => good(x) && maybe(x) }

You can't really use andThen because composition is like the transitive property.

[(A => Boolean) && (A => Boolean)] != [(A => B) => C]
// ^ What you want                     ^ Composition

Upvotes: 4

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