Match String with List Items - scala

Question

I have a list and two strings :
val features = List("one","two","three")
val strOne = "one_five"
val strTwo = "seven_five"
I'd like to match each string to items of the list.
If beginning of string matches one of list items then print matched list item and string itself.
If not, nothing to print.
I have method that I think make what I need but I cannot compile it :
def getElement(any: String): String = any match {
case s :: rest if features.contains(s) => s + "= " + any
case _ => // Nothing
}
I wanted the following :
scala> getElement(strOne)
"one_five= one"
scala> getElement(strTwo)

Answer 1

You can't just return nothing. You promised that your method would return a String, so you must return one. You can either return an Option[String] (preferred) or return Unit and do the printing yourself. Further, the built in method TraversableLike#find will do part of the job.
def findFeature(str: String): Option[String] = features.find(_ startsWith str) map { value => s"$str=$value" }
In order to get the printing behavior:
findFeature(str) foreach println
// or redefine findFeature similarly
Further, you seem to misunderstand pattern matching: You don't want to match on the string; you want to match the list's elements against the string. Here's a version that uses pattern matching:
def getElement(feature: String): Option[String] = {
#tailrec def getElem0(feature: String, strs: List[String]): Option[String] = strs match {
case s :: _ if s startsWith feature => Some(s"$feature=$s") // Matching case
case _ :: rest => getElem0(feature, rest) // Not matched, but more to search
case Nil => None // Empty list; failure
}
getElem0(feature, features)
}

Answer 2

Your solution can't compile because :: is a List method, and s is a String. Moreover, getElement is declared to return a String therefore it should return a String for any input. So you can't just return "nothing" in the second case.
Here's an alternative implementation:
def printElement(any: String): Unit = features
.find(s => any.startsWith(s)) // find matching (returns Option[String])
.foreach(s => println(s + "= "+ any)) // print if found
printElement(strOne) // one= one_five
printElement(strTwo)

Answer 3

Simple one line Scala code
Find in list the item who's first part is present in the list
features.find(_ == str.split("_")(0)).map { elem => s"$str= $elem"}.getOrElse("")
Put the above line inside the function.
def getElement(str: String): String = features.find(_ == str.split("_")(0)).map { elem => s"$str= $elem"}.getOrElse("")
Scala REPL
scala> val strOne = "one_five"
strOne: String = one_five
scala> val str = "one_five"
str: String = one_five
scala> features.find(_ == str.split("_")(0)).getOrElse("")
res2: String = one
scala> features.find(_ == str.split("_")(0)).map(elem => s"$str= $elem").getOrElse("")
res3: String = one_five= one