Tour of Scala
Regular Expression Patterns
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Regular expressions are strings which can be used to find patterns (or lack thereof) in data. Any string can be converted to a regular expression using the .r method.
import scala.util.matching.Regex
val numberPattern: Regex = "[0-9]".r
numberPattern.findFirstMatchIn("awesomepassword") match {
case Some(_) => println("Password OK")
case None => println("Password must contain a number")
}
import scala.util.matching.Regex
val numberPattern: Regex = "[0-9]".r
numberPattern.findFirstMatchIn("awesomepassword") match
case Some(_) => println("Password OK")
case None => println("Password must contain a number")
In the above example, the numberPattern is a Regex
(regular expression) which we use to make sure a password contains a number.
You can also search for groups of regular expressions using parentheses.
import scala.util.matching.Regex
val keyValPattern: Regex = "([0-9a-zA-Z- ]+): ([0-9a-zA-Z-#()/. ]+)".r
val input: String =
"""background-color: #A03300;
|background-image: url(img/header100.png);
|background-position: top center;
|background-repeat: repeat-x;
|background-size: 2160px 108px;
|margin: 0;
|height: 108px;
|width: 100%;""".stripMargin
for (patternMatch <- keyValPattern.findAllMatchIn(input))
println(s"key: ${patternMatch.group(1)} value: ${patternMatch.group(2)}")
import scala.util.matching.Regex
val keyValPattern: Regex = "([0-9a-zA-Z- ]+): ([0-9a-zA-Z-#()/. ]+)".r
val input: String =
"""background-color: #A03300;
|background-image: url(img/header100.png);
|background-position: top center;
|background-repeat: repeat-x;
|background-size: 2160px 108px;
|margin: 0;
|height: 108px;
|width: 100%;""".stripMargin
for patternMatch <- keyValPattern.findAllMatchIn(input) do
println(s"key: ${patternMatch.group(1)} value: ${patternMatch.group(2)}")
Here we parse out the keys and values of a String. Each match has a group of sub-matches. Here is the output:
key: background-color value: #A03300
key: background-image value: url(img/header100.png)
key: background-position value: top center
key: background-repeat value: repeat-x
key: background-size value: 2160px 108px
key: margin value: 0
key: height value: 108px
key: width value: 100
Moreover, regular expressions can be used as patterns (in match expressions) to conveniently extract the matched groups:
def saveContactInformation(contact: String): Unit = {
import scala.util.matching.Regex
val emailPattern: Regex = """^(\w+)@(\w+(.\w+)+)$""".r
val phonePattern: Regex = """^(\d{3}-\d{3}-\d{4})$""".r
contact match {
case emailPattern(localPart, domainName, _) =>
println(s"Hi $localPart, we have saved your email address.")
case phonePattern(phoneNumber) =>
println(s"Hi, we have saved your phone number $phoneNumber.")
case _ =>
println("Invalid contact information, neither an email address nor phone number.")
}
}
saveContactInformation("123-456-7890")
saveContactInformation("[email protected]")
saveContactInformation("2 Franklin St, Mars, Milky Way")
def saveContactInformation(contact: String): Unit =
import scala.util.matching.Regex
val emailPattern: Regex = """^(\w+)@(\w+(.\w+)+)$""".r
val phonePattern: Regex = """^(\d{3}-\d{3}-\d{4})$""".r
contact match
case emailPattern(localPart, domainName, _) =>
println(s"Hi $localPart, we have saved your email address.")
case phonePattern(phoneNumber) =>
println(s"Hi, we have saved your phone number $phoneNumber.")
case _ =>
println("Invalid contact information, neither an email address nor phone number.")
saveContactInformation("123-456-7890")
saveContactInformation("[email protected]")
saveContactInformation("2 Franklin St, Mars, Milky Way")
The output would be:
Hi, we have saved your phone number 123-456-7890.
Hi JohnSmith, we have saved your email address.
Invalid contact information, neither an email address nor phone number.