Scala generic "string split" method

Question

If I were splitting a string, I would be able to do

"123,456,789".split(",")

to get Seq("123","456","789")

Thinking of a string as a sequence of characters, how could this be generalized to other sequences of objects?

val x = Seq(One(),Two(),Three(),Comma(),Five(),Six(),Comma(),Seven(),Eight(),Nine())
x.split(
  number=>{
    case _:Comma => true
    case _ => false
  }
)

split in this case doesn't exist, but it reminds me of span, partition, groupby, but only span seems close, but it doesn't handle leading/ending comma's gracefully.

Federico Pellegatta · Accepted Answer · 2017-03-08 18:47:27Z

1

implicit class SplitSeq[T](seq: Seq[T]){
  import scala.collection.mutable.ListBuffer
  def split(sep: T): Seq[Seq[T]] = {
    val buffer = ListBuffer(ListBuffer.empty[T])
    seq.foreach {
      case `sep` => buffer += ListBuffer.empty
      case elem => buffer.last += elem
    }; buffer.filter(_.nonEmpty)
  }
}

It can be then used like x.split(Comma()).

answered Mar 8, 2017 at 18:47

Federico Pellegatta

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1 Comment

Ryan Leach Over a year ago

Accepted this over Meghana's as it seems more readable to me + it doesn't need multiple tuple2 creation.

Meghana Viswanath · Accepted Answer · 2017-03-08 15:22:29Z

1

The following is 'a' solution, not the most elegant -

def split[A](x: Seq[A], edge: A => Boolean): Seq[Seq[A]] = { 

  val init = (Seq[Seq[A]](), Seq[A]())

  val (result, last) = x.foldLeft(init) { (cum, n) =>
    val (total, prev) = cum

    if (edge(n)) {
        (total :+ prev, Seq.empty)
    } else {
        (total, prev :+ n)
    }
  }

  result :+ last
}

Example result -

scala> split(Seq(1,2,3,0,4,5,0,6,7), (_:Int) == 0)
res53: Seq[Seq[Int]] = List(List(1, 2, 3), List(4, 5), List(6, 7))

answered Mar 8, 2017 at 15:22

Meghana Viswanath

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Comments

Ryan Leach · Accepted Answer · 2017-03-08 14:24:11Z

0

This is how I've solved it in the past, but I suspect there is a better / more elegant way.

  def break[A](xs:Seq[A], p:A => Boolean): (Seq[A], Seq[A]) = {
    if (p(xs.head)) {
      xs.span(p)
    }
    else {
      xs.span(a => !p(a))
    }
  }

answered Mar 8, 2017 at 14:24

Ryan Leach

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