Scala - Convert List[String] to tuple List[(Int, Int)]

Question

I would like to getLine from a Source and convert it to a tuple (Int, Int). I've did it using foreach.

       val values = collection.mutable.ListBuffer[(Int, Int)]()

        Source.fromFile(invitationFile.ref.file).getLines().filter(line => !line.isEmpty).foreach(line => {
          val value = line.split("\\s")

          values += ((value(0).toInt, (value(1).toInt)))
        })

What's the best way to write the same code without use foreach?

score 3 · Accepted Answer · edited Dec 05 '16 at 15:56

3

Use map, it builds a new list for you:

Source.fromFile(invitationFile.ref.file)
.getLines()
.filter(line => !line.isEmpty)
.map(line => {
  val value = line.split("\\s")
  (value(0).toInt, value(1).toInt)
})
.toList()

edited Dec 05 '16 at 15:56

Ven

19,015
2
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answered Nov 07 '16 at 18:15

score 0 · Answer 2 · answered Nov 07 '16 at 18:15

foreach should be a final operation, not a transformation.

In your case, you want to use the function map

val values = Source.fromFile(invitationFile.ref.file).getLines()
  .filter(line => !line.isEmpty)
  .map(line => line.split("\\s"))
  .map(line => (line(0).toInt, line(1).toInt))

score 0 · Answer 3 · answered Nov 07 '16 at 18:44

0

Using a for comprehension:

val values = for(line <- Source.fromFile(invitationFile.ref.file).getLines(); if !line.isEmpty) {
  val splits = line.split("\\s")
  yield (split(0).toInt, split(1).toInt)
}

answered Nov 07 '16 at 18:44

David Weiser

5,190
4
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when should someone choose a `for` comprehension vs a `map` ? – Tyler Nov 07 '16 at 18:48
`for`s are syntactic sugar. See http://stackoverflow.com/questions/1052476/what-is-scalas-yield/1059501#1059501. They'll get compiled into `map` calls (among other calls). I find `for`s easier to read then a bunch of chained `map` calls. – David Weiser Nov 07 '16 at 18:52

Scala - Convert List[String] to tuple List[(Int, Int)]

3 Answers3