Scala regex ignorecase

Question

I am trying to match the Roman number from the I to IX with a regex.

val pattern = "(\\sI\\s|\\sII\\s|\\sIII\\s|\\sIV\\s|\\sV\\s|\\sVI\\s|\\sVII\\s|\\sVIII\\s|\\sIX\\s)".r

This can only matches the upper case. I want to ignore the case.

My test string is "Mark iii ".

Answer 1

Try something like this:

"\\s(?i)(?:I{1,3}|IV|VI{0,3}|I?X)\\s"

where the (?i) enables case insensitive matching.

Note that you might want to use word boundaries instead of space chars:

"\\b(?i)(?:I{1,3}|IV|VI{0,3}|I?X)\\b"

otherwise "Mark iii." won't match.

Answer 2

Use the Java regex special construct (?i) at the front of your regex for case-insensitive matching:

val patternic = """(?i)(\sI\s|\sII\s|\sIII\s|\sIV\s|\sV\s|\sVI\s|\sVII\s|\sVIII\s|\sIX\s)""".r

Example in scala interpreter:

scala>   val pattern =
"""(\sI\s|\sII\s|\sIII\s|\sIV\s|\sV\s|\sVI\s|\sVII\s|\sVIII\s|\sIX\s)""".r
pattern: scala.util.matching.Regex = (\sI\s|\sII\s|\sIII\s|\sIV\s|\sV\s|\sVI\s|\sVII\s|\sVIII\s|\sIX\s)

scala>   pattern findPrefixMatchOf " VI "
res3: Option[scala.util.matching.Regex.Match] = Some( VI )

scala>   pattern  findPrefixMatchOf " vi "
res6: Option[scala.util.matching.Regex.Match] = None

scala>   val patternic = """(?i)(\sI\s|\sII\s|\sIII\s|\sIV\s|\sV\s|\sVI\s|\sVII\s|\sVIII\s|\sIX\s)""".r
patternic: scala.util.matching.Regex = (?i)(\sI\s|\sII\s|\sIII\s|\sIV\s|\sV\s|\sVI\s|\sVII\s|\sVIII\s|\sIX\s)

scala>   patternic findPrefixMatchOf " VI "
res7: Option[scala.util.matching.Regex.Match] = Some( VI )


scala>   patternic findPrefixMatchOf " vi "
res9: Option[scala.util.matching.Regex.Match] = Some( vi )

Answer 3

I recently was provided with a very long case insensitive Java regex, I decided just not mess with it and left it as it is. It's a Java approach, but it can be used in Scala too.

import java.util.regex.Pattern

val EmailPattern = Pattern.compile(
  "PatternGoesHere", 
  Pattern.CASE_INSENSITIVE
)
val result = EmailPattern.matcher("StringToMatch").matches()