Retrieving Values from a Seq based on a condition - arrays

Question

I have the below Seq with me
scala> var al = Seq((1.0, 20.0, 100.0), (2.0, 30.0, 100.0), (1.0, 11.0, 100.0), (1.0, 20.0, 100.0), (1.0, 10.0, 100.0),(2.0,9.0,100.0))
al: Seq[(Double, Double, Double)] = List((1.0,20.0,100.0), (2.0,30.0,100.0), (1.0,11.0,100.0), (1.0,20.0,100.0), (1.0,10.0,100.0), (2.0,9.0,100.0))
How to take from this Seq the first n elements where - sum of the second item is greater than 60 percent of the third item(this will be a constant value)
Expected Output -
scala> Seq((1.0, 20.0, 100.0), (2.0, 30.0, 100.0), (1.0, 11.0, 100.0))
res30: Seq[(Double, Double, Double)] = List((1.0,20.0,100.0), (2.0,30.0,100.0), (1.0,11.0,100.0))
Edit -1
I have done this with some ugly way. But if there is any beautiful functional way of solving this would be great. I would really need to get rid of this counters and is little bit tricky for me.
var counter =0d ; var sum = 0d
var abc :Seq[Double] = for (x <- al) yield {
counter+=1 ;sum = sum + x._2 ;
if (sum > 60) counter else 0
}
println(al.take(abc.filterNot(_==0).min.toInt))

Answer 1

If you're on Scala 2.13.x then you might unfold():
Seq.unfold((al,0.0)){ case (lst,sum) =>
Option.when(lst.nonEmpty && sum < 0.6 * lst.head._3) {
(lst.head, (lst.tail, sum + lst.head._2))
}
}
//res0: Seq[(Double, Double, Double)] =
// List((1.0,20.0,100.0), (2.0,30.0,100.0), (1.0,11.0,100.0))
On earlier Scala versions you could scanLeft() to calculate the sums and use that to count how many elements to take().
val cnt = al.view
.scanLeft(0.0)(_ + _._2)
.takeWhile(_ < 0.6 * al.headOption.getOrElse((0d,0d,0d))._3)
.length
al.take(cnt)

Answer 2

You can use recursive function with accumulator to get needed number of elements:
def getIndex(input: Seq[(Double,Double,Double)], index: Int = 0, sum: Double = 0.0): Int = {
input match {
case Seq() => index
case Seq(head, _#_*) if head._2 + sum > head._3 * 0.6 => index + 1
case Seq(head, tail#_*) => getIndex(tail, index + 1, sum + head._2)
}
}
al.take(getIndex(al))
Or to build a list:
def getList(input: Seq[(Double,Double,Double)], sum: Double = 0.0): List[(Double,Double,Double)] = {
input match {
case Seq() => List.empty
case Seq(head, _#_*) if head._2 + sum > head._3 * 0.6 => head :: List.empty
case Seq(head, tail#_*) => head :: get(tail, sum + head._2)
}
}
getList(al)
As mentioned in comments - restricting al to List can allow using :: which should be more efficient:
def get(input: List[(Double,Double,Double)], sum: Double = 0.0): List[(Double,Double,Double)] = {
input match {
case Seq() => List.empty
case head :: tail if head._2 + sum > head._3 * 0.6 => head :: List.empty
case head :: tail => head :: get(tail, sum + head._2)
}
}