How to add List of Option of doubles in scala

Question

I have a list of option like so,

var data = List(
  List(Some(313.062468), Some(27.847252)),
  List(Some(301.873641), Some(42.884065)),
  List(Some(332.373186), Some(53.509768))
)

And I'd like to sum all the values of each nested list.

I have the following code which doesn't work:

return data.flatten.foldLeft((Some(0), Some(0))) {
  case ((accA, accB), (a, b)) => {
    (_ + a, _ + b)
  }
}

What should happen if one or both of the options is a `None` instead of a `Some`? — Jesper, Nov 18 '16 at 10:43
@pamu No, I'm asking Naseebullah what he wants in that case, because it's not automatically clear. Should `None` be treated as zero? Or should something else happen? — Jesper, Nov 18 '16 at 10:44

Nagarjuna Pamu · Accepted Answer · 2016-11-18T10:55:44.447

Flatten, Collect and Sum

Flatten, collect and sum

data.flatten.collect { case Some(value) => value }.sum

Scala REPL

scala> var data = List(
     |   List(Some(313.062468), Some(27.847252)),
     |   List(Some(301.873641), Some(42.884065)),
     |   List(Some(332.373186), Some(53.509768))
     | )
data: List[List[Some[Double]]] = List(List(Some(313.062468), Some(27.847252)), List(Some(301.873641), Some(42.884065)), List(Some(332.373186), Some(53.509768)))

scala>

scala> data.flatten
res2: List[Some[Double]] = List(Some(313.062468), Some(27.847252), Some(301.873641), Some(42.884065), Some(332.373186), Some(53.509768))

scala> data.flatten.collect { case Some(value) => value }.sum
res3: Double = 1071.55038

Option is iterable

Looks quite neat.

data.iterator.flatMap(_.iterator.flatMap(_.iterator)).sum

Scala REPL

scala> data.iterator.flatMap(_.iterator.flatMap(_.iterator)).sum
res5: Double = 1071.55038

For comprehension

(for {
  list <- data.iterator
  elem <- list.iterator
  value <- elem.iterator
  } yield value).sum

Thank you! And what if i only want to sum only the first nested list? — S. Nas, Nov 18 '16 at 10:43
@NaseebullahSafi if you need only first list sum ...just get the head of the list and do that same process. `data.head.collect { case Some(value) => value }.sum` — Nagarjuna Pamu, Nov 18 '16 at 10:48

How to add List of Option of doubles in scala

1 Answers1

Flatten, Collect and Sum

Option is iterable

For comprehension