Can I output a collection instead of a tuple in Scalding map method?

Question

If you want to create a pipe with more than 22 fields from a smaller one in Scalding you are limited by Scala tuples, which cannot have more than 22 items.

Is there a way to use collections instead of tuples? I imagine something like in the following example, which sadly doesn't work:

input.read.mapTo('line -> aLotOfFields) { line: String =>
  (1 to 24).map(_.toString)
}.write(output)

Keratoid

Answer 1

actually you can. It's in FAQ - https://github.com/twitter/scalding/wiki/Frequently-asked-questions#what-if-i-have-more-than-22-fields-in-my-data-set

val toFields = (1 to 24).map(f => Symbol("field_" + f)).toList

input
  .read
  .mapTo('line -> toFields) { line: String =>
    new Tuple((1 to 24).map(_.toString).map(_.asInstanceOf[AnyRef]): _*)

  }

the last map(_.asInstanceOf[AnyRef]) looks ugly so if you find better solution let me know please.

Postdiluvian

Answer 2

Wrap your tuples into case classes. It will also make your code more readable and type safe than using tuples and collections respectively.

Melosa