Scala: Split array into chunks by some logic

Question

Is there some predefined function in Scala to split list into several lists by some logic? I found grouped method, but it doesn't fit my needs.

For example, I have List of strings: List("questions", "tags", "users", "badges", "unanswered").

And I want to split this list by max length of strings (for example 12). In other words in each resulting chunk sum of the length of all strings should not be more than 12:

List("questions"), List("tags", "users"), List("badges"), List("unanswered")

EDIT: I'm not necessarily need to find the most optimal way of combining strings into chunks, just linear loop which checks next string in list, and if its length doesn't fit to required (12) then return current chunk and next string will belong to next chunk

Pretty much a duplicate of this: stackoverflow.com/questions/27122150/… — The Archetypal Paul
– The Archetypal Paul, Commented Sep 29, 2015 at 19:34

Sascha Kolberg · Accepted Answer · 2015-09-29 19:12:51Z

7

There is no buildIn mechanism to do that, that I know of, but you could achieve something like that with a foldLeft and bit of coding:

val test = List("questions", "tags", "users", "badges", "unanswered")

test.foldLeft(List.empty[List[String]]) {
  case ((head :: tail), word) if head.map(_.length).sum + word.length < 12 =>
    (word :: head) :: tail
  case (result, word) =>
    List(word) :: result
}

-> res0: List[List[String]] = List(List(unanswered), List(badges), List(users, tags), List(questions))

answered Sep 29, 2015 at 19:12

Sascha Kolberg

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1 Comment

Łukasz Over a year ago

if order is important you should reverse result after fold like this result.map(_.reverse).reverse

jbrown · Accepted Answer · 2016-07-26 10:18:48Z

1

If you can make reasonable assumptions about the max length of a string (e.g. 10 characters), you could then use sliding which is much faster for a long list:

val elementsPerChunk = ???   // do some maths like 
                             // CHUNK_SIZE / MAX_ELEM_LENGTH
val test = List("questions", "tags", "users", "badges", "unanswered")
test.sliding(elementsPerChunk, elementsPerChunk).toList

answered Jul 26, 2016 at 10:18

jbrown

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