Matching or regular expression in scala

Question

I have a regular expression like ".*(A20).*|.*(B30).*|C" . I would like to write a function its returns A20 or B30 based on the match found.

val regx=".*(A20).*|.*(B30).*".r

"helloA20" match { case regx(b,_) => b; case _ => "" } // A20
"helloB30" match { case regx(b,_) => b; case _ => "" } // null
 "C" match { case regx(b,_) => b case _ => "" }

It's returning null because I am not considering the second group. In my actual code, I have a lot of group like that. I would like to return the matched string. Please help me to find a solution.

Answer 1

Easy! It should be like this:

val regx="^(.*(B30|A20).*|(C))$".r

Demo: https://regex101.com/r/nA6dQ9/1

Then you get the second value in the array of every group.

That way you only have one group regardless of the many possibilities.

Answer 2

You're close:

def extract(s: String) = s match {
 case regx(b, _) if b != null => b
 case regx(_, b) if b != null => b
 case _ => "" 
}

extract("helloA20")
res3: String = A20

extract("helloB30")
res4: String = B30

extract("A30&B30")
res6: String = B30

If you have a lot of groups, it's reasonable to use for comprehension insted of pattern matching. This code will return first match or None:

val letters = ('A' to 'Z').toSeq
val regex = letters.map(_.toString).mkString("(", "|", ")").r

def extract(s: String) = {
  for {
    m <- regex.findFirstMatchIn(s)
  } yield m.group(1)
}

extract("A=B=")
extract("dsfdsBA")
extract("C====b")
extract("a====E")

res0: Option[String] = Some(A)
res1: Option[String] = Some(B)
res2: Option[String] = Some(C)
res3: Option[String] = Some(E)