Partition a collection into “k” close-to-equal pieces (Scala, but language agnostic)

Question

Defined before this block of code:

• dataset can be a Vector or List
• numberOfSlices is an Int

Answer 1

Here is my take on the problem:

  def partition[T](items: Seq[T], partitionsCount: Int): List[Seq[T]] = {
    val minPartitionSize = items.size / partitionsCount
    val extraItemsCount = items.size % partitionsCount

    def loop(unpartitioned: Seq[T], acc: List[Seq[T]], extra: Int): List[Seq[T]] =
      if (unpartitioned.nonEmpty) {
        val (splitIndex, newExtra) = if (extra > 0) (minPartitionSize + 1, extra - 1) else (minPartitionSize, extra)
        val (newPartition, remaining) = unpartitioned.splitAt(splitIndex)
        loop(remaining, newPartition :: acc, newExtra)
      } else acc

    loop(items, List.empty, extraItemsCount).reverse
  }

It's more verbose than some of the other solutions but hopefully more clear as well. reverse is only necessary if you want the order to be preserved.