Question

I have a csv with column headings. One column heading is “DATE”. If I want to generate two CSVs split into before DATE and after/including DATE is there a way to do this without procedurally looping? I have noticed most of the list functions are suited for filtering by row.

Answer 1

I’ll assume you already have your data parsed into something like this:

val myDoc = List(
  List("ID", "NAME", "DATE", "DESC"),
  List("1", "a", "1990", "x"), 
  List("2", "b", "1991", "y")
)

Now we can use splitAt and unzip to pull the list apart. Note that I’m assuming a lot about the data—in real code we’d want to check that the list is non-empty and that the header actually contains a "DATE" column.

def split(doc: Seq[Seq[String]]) = {
  val i = doc.head.indexOf("DATE")
  doc.map(_.splitAt(i)).unzip
}

We can apply it to our test data:

scala> val (b, a) = split(myDoc)
b: List[Seq[String]] = List(List(ID, NAME), List(1, a), List(2, b))
a: List[Seq[String]] = List(List(DATE, DESC), List(1990, x), List(1991, y))

This looks reasonable to me.