Scala regex pattern extractor

Question

What am I doing wrong here:

val pattern = "([1-7]),([0-1][0-9]|[2][0-3])([0-1][0-9]|[2][0-3])".r
val pattern(count, fruit) = "7,2323"

gives:

[info]   Scenario: For a set of combination of hour formats, map them to the expected 24 hours format1 *** FAILED ***
[info]   scala.MatchError: 7,2323 (of class java.lang.String)
[info]   at com.mf.location.os.service.util.HoursFormatUtil$.fromHours(HoursFormatUtil.scala:55)
[info]   at com.mf.location.os.service.util.HoursFormatUtilSpec.$anonfun$new$9(HoursFormatUtilSpec.scala:71)
[info]   at org.scalatest.OutcomeOf.outcomeOf(OutcomeOf.scala:85)
[info]   at org.scalatest.OutcomeOf.outcomeOf$(OutcomeOf.scala:83)
[info]   at org.scalatest.OutcomeOf$.outcomeOf(OutcomeOf.scala:104)
[info]   at org.scalatest.Transformer.apply(Transformer.scala:22)
[info]   at org.scalatest.Transformer.apply(Transformer.scala:20)
[info]   at org.scalatest.featurespec.AnyFeatureSpecLike$$anon$1.apply(AnyFeatureSpecLike.scala:257)
[info]   at org.scalatest.TestSuite.withFixture(TestSuite.scala:196)
[info]   at org.scalatest.TestSuite.withFixture$(TestSuite.scala:195)

However println(s"matches ${pattern.matches("7,2323")}") returns true.

question from:https://stackoverflow.com/questions/66055991/scala-regex-pattern-extractor

Answer 1

If your count value should be 7 and the fruit value should be 2323, you can use

val pattern = "([1-7]),((?:[0-1][0-9]|2[0-3]){2})".r
val line = "7,2323"
val (count, fruit) = line match {
  case pattern(count, fruit) => (count,fruit)
  case _ => ("","")
}
println(s"${count} and ${fruit}")
// => 7 and 2323

See the Scala demo.

Note the ([1-7]),((?:[0-1][0-9]|2[0-3]){2}) refactored pattern that now contains only two capturing groups. pattern(count, fruit) "extracts" the capturing group values and assigns them to count and fruit. If there is no match, these variable will be empty strings.