Read a tuple from a file in Scala - scala

Question

my Task is to read registrations from a file given like:
Keri,345246,2
Ingar,488058,2
Almeta,422016,1
and insert them into a list(Tuple of (String, Int, Int).
So far I wrote this:
The problem is that I don‘t understand why I can't try to cast value2 and value3 to Int even tho they should be Strings because they come from an Array of Strings. Could someone tell me, what my mistake is, I am relatively new to Scala

Answer 1

What is the point of using Scala if you are going to write Java code?
This is how you would properly read a file as a List of case classes.
import scala.io.Source
import scala.util.Using
// Use proper names for the fields.
final case class Registration(field1: String, field2: Int, field3: Int)
// You may change the error handling logic.
def readRegistrationsFromFile(fileName: String): List[Registration] =
Using(Source.fromFile(fileName)) { source =>
source.getLines().map(line => line.split(',').toList).flatMap {
case field1Raw :: field2Raw :: field3Raw :: Nil =>
for {
field2 <- field2Raw.toIntOption
field3 <- field3Raw.toIntOption
} yield Registration(field1 = field1Raw.trim, field2, field3)
case _ =>
None
}.toList
}.getOrElse(default = List.empty)
(feel free to ask any question you may have about this code)

Answer 2

In Scala, in order to convert a String to an Int you need explicit casting.
This can be achieved like this if you are sure the string can be parsed into a integer:
val values = values(1).toInt
If you cannot trust the input (and you probably should not), you can use .toIntOption which will give you a Option[Int] defined if the value was converted successfully or undefined if the string did not represent an integer.

Answer 3

The previous answers are correct. I would add a few more points.
saveContent is declared as a val. This is means it cannot be changed (assigned another value). You can use the Scala REPL (command-line) tool to check:
scala> val saveContent = Nil
val v: collection.immutable.Nil.type = List()
scala> saveContent = 3
^
error: reassignment to val
Instead, you could use a var, although it would be more idiomatic to have an overall pattern like the one provided by Luis Miguel's answer - with pattern-matching and a for-comprehension.
You can use the Scala REPL to check the types of the variables, too. Splitting a String will always lead to more Strings, not Ints, etc.
> val values = "a,2,3".split(",")
val values: Array[String] = Array(a, 2, 3)
> values(2)
val res3: String = 3
This is why a cast like Gael's is necessary.
Array-type access is done with parentheses and not square brackets, in Scala. See above, and http://scalatutorials.com/tour/interactive_tour_of_scala_lists for more details.