Geek Answers Handbook

How to break a list into groups by week in scala

case class Test(dayOfWeek:Int,b:Int=Random.nextInt)
val data=(3 to 100).map(_ % 7).map(Test(_))

how to divide the data into groups, each group has one week of data, if the week is not completed, there is also a group. So the group should be

Group 1: (3,4,5,6)   // the number here is the dayOfWeek
Group 2: (0,1,2,3,4,5,6)
Group 3: (0,1,2,3,4,5,6)
...
last Group:(0,1,2)
+4
source share
3 answers

Scala collections are really powerful, this should do it in a few lines:

val (firstWeek, nextWeeks) = data.span(_.dayOfWeek != 0)
val weeks = (firstWeek :: nextWeeks.grouped(7).toList).dropWhile(_.isEmpty)

Take a look at the document for spanand grouped here .

println(weeks.zipWithIndex.map {
  case (week, i) => s"Group $i: (${week.map(_.dayOfWeek).mkString(",")})"
}.mkString("\n"))

outputs:

Group 0: (3,4,5,6)
Group 1: (0,1,2,3,4,5,6)
Group 2: (0,1,2,3,4,5,6)
[snip]
Group 12: (0,1,2,3,4,5,6)
Group 13: (0,1,2,3,4,5,6)
Group 14: (0,1,2)
+4
source

You can do this with a fold:

case class Test(dayOfWeek: Int, b: Int = scala.util.Random.nextInt)
val data = (3 to 100).map(_ % 7).map(Test(_))

val spans =
  data.foldLeft(Vector(Vector.empty[Test])) {
    case (zs :+ z, e) =>
      if (e.dayOfWeek == 0)
        if (z.nonEmpty)
          (zs :+ z) :+ Vector(e)
        else
          zs :+ Vector(e)
      else
        zs :+ (z :+ e)
  }

for ((g, i) <- spans.zipWithIndex) {
  println(f"Group $i: (${g.map(_.dayOfWeek).mkString(",")})")
}

Conclusion:

Group 0: (3,4,5,6)
Group 1: (0,1,2,3,4,5,6)
Group 2: (0,1,2,3,4,5,6)
Group 3: (0,1,2,3,4,5,6)
Group 4: (0,1,2,3,4,5,6)
Group 5: (0,1,2,3,4,5,6)
Group 6: (0,1,2,3,4,5,6)
Group 7: (0,1,2,3,4,5,6)
Group 8: (0,1,2,3,4,5,6)
Group 9: (0,1,2,3,4,5,6)
Group 10: (0,1,2,3,4,5,6)
Group 11: (0,1,2,3,4,5,6)
Group 12: (0,1,2,3,4,5,6)
Group 13: (0,1,2,3,4,5,6)
Group 14: (0,1,2)
+2
source

, weekDay.

def groupByWeek[T](s: Seq[T], maxDay: Int = 6, weekDay: T => Int) = {
  @scala.annotation.tailrec
  def recurse(r: Seq[T], results: Seq[Seq[T]]): Seq[Seq[T]] =
    r.splitAt(r.indexWhere(item => weekDay(item) == maxDay)) match {
      case (hd, tl) if (hd.isEmpty && tl.isEmpty) => results
      case (hd, tl) if (hd.isEmpty) => results :+ tl
      case (hd, tl) => recurse(tl.tail, results :+ (hd :+ tl.head))
    }
  recurse(s,Seq.empty)
  }
}

:

val weeks = groupByWeek(data, weekDay = (x:Test) => x.dayOfWeek)

:

println(weeks.zipWithIndex.map {
  case (week, i) => s"Group $i: (${week.map(_.dayOfWeek).mkString(",")})"
}.mkString("\n"))

:

Group 0: (3,4,5,6)
Group 1: (0,1,2,3,4,5,6)
Group 2: (0,1,2,3,4,5,6)
[snip]
Group 12: (0,1,2,3,4,5,6)
Group 13: (0,1,2,3,4,5,6)
Group 14: (0,1,2)
+2

More articles:


All Articles