How to combine filter and map in Scala?

Question

I have List[Int] in Scala. The List is List(1,2,3,4,5,6,7,8,9,10). I want to filter the list so that it only has even numbers. And I w

Answer 1

As @cmbaxter said, collect suits your need perfectly. The other nice thing about collect is that it figures out resulting type in case you're filtering by class:

scala> trait X
// defined trait X

scala> class Foo extends X
// defined class Foo

scala> class Bar extends X
// defined class Bar

scala> val xs = List(new Foo, new Bar, new Foo, new Bar)
// xs: List[X] = List(Foo@4cfa8227, Bar@78226c36, Foo@3f685162, Bar@11f406f8)

scala> xs.collect { case x: Foo => x }
// res1: List[Foo] = List(Foo@4cfa8227, Foo@3f685162)

On par, filter can't be that smart (see List[Foo] vs List[X]):

scala> xs.filter { case x: Foo => true; case _ => false }
// res3: List[X] = List(Foo@4cfa8227, Foo@3f685162)