How do I match Regex Pattern on List to filter out decimal elements in Scala

Question

I am wondering without creating a function, how can I filter out numbers from a list with both numbers and strings:

val a = sc.parallelize(List(“cat”,“horse”,4.0,3.5,2,“dog”))

I believe my question indeed is looking for how to use regex in Scala to find out matched pattern

----Updated on 20180302 11pm EST: Thanks to @Nyavro which is the closest answer, I slightly modified as below:

val doubles = a.collect {
  case v: Double => v
  case v: Int => v
}

Now I get:

res10: Array[Double] = Array(4.0, 3.5, 2.0)

Just be curious, can types be mixed in a collect result in Scala?

Thanks to all replies.

Answer 1

Use collect:

val doubles = a.collect {
  case v: Double => v
}

Answer 2

To filter for elements of type Int and Double , and to retain their respective types, you might try this.

a.flatMap {
  case v: Int => Some(v)
  case v: Double => Some(v)
  case _ => None
}
//res0: List[AnyVal] = List(4.0, 3.5, 2)

To help understand why this is a really bad idea, read this question , and its answers.

Answer 3

You can use isInstanceOf to check whether an element of your list is a string.

val l = List("cat","horse",4.0,3.5,2,"dog")
l.filter(_.isInstanceOf[String])
>> List[Any] = List(cat, horse, dog)

Regex is (largely) irrelevant here because you do not have strings, you have a List[Any] that you're turning into an RDD[Any] . (The RDD is largely irrelevant here, too, except RDDs have no filterNot and Lists do--I can't tell if you want to keep the strings or drop the strings.)

Note also that filter takes a function as an argument--having some function here is inescapable, even if it's anonymous, as it is in my example.

I have an inkling, though, that I've given an answer to the opposite of what you're asking, and you have an RDD[String] that you want to convert to RDD[Double] , throwing away the strings that don't convert. In that case, I would try to convert the strings to doubles, wrapping that in a Try and check for success, using the result to filter:

def isDouble(s: String) = Try(s.toDouble).isSuccess