Randomly distribute N items across M buckets

buckets.scala

package example

import scala.util.Random

object Hello extends App {
  val items                        = (0 to 10).toList.map(i => s"Item $i")
  val numberOfBuckets              = 10
  val working: Map[String, Double] = items.map(i => (i, Random.nextDouble())).toMap

  val bucketSize                            = 1.0 / numberOfBuckets
  val buckets: Map[Int, Iterable[String]]   = working.groupMap { case (item, rnd) => (rnd / bucketSize).toInt }(_._1)
  val sorted: List[(Int, Iterable[String])] = buckets.toList.sortBy(_._1).toList

  println(
    sorted
      .map { case (bucket, items) =>
        s"Bucket $bucket: ${items.mkString(",")}"
      }
      .mkString("\n")
  )
}

Example output:

Bucket 0: Item 8
Bucket 2: Item 4,Item 3,Item 9
Bucket 3: Item 7,Item 2,Item 6
Bucket 6: Item 5,Item 0,Item 10
Bucket 7: Item 1

Bucket 1: Item 4
Bucket 2: Item 9
Bucket 3: Item 5,Item 7
Bucket 5: Item 0
Bucket 6: Item 10,Item 6
Bucket 7: Item 8,Item 3
Bucket 8: Item 1,Item 2