poisson.scala

import scala.util.Random

object Bootstrap {
  def generate[T](seed: T, numBootStraps: Int): Iterator[Int] = {
    val rng = new Random(seed.hashCode())
    (0 until numBootStraps)
      .toIterator
      .map(_ => samplePoisson(rng, 1.0))
  }

  def samplePoisson(rng: Random, lambda: Double): Int = {
    val expLambda = math.exp(-lambda)
    var k = 0
    var p = 1.0

    do {
      k += 1
      p *= rng.nextDouble()
    } while (p > expLambda)

    k - 1
  }
}

val a = (1 to 100).flatMap(i => Bootstrap.generate(i, 30).toList.zipWithIndex).groupBy(_._2).mapValues(v => v.map(_._1).sum).values
a.sum / a.size.toDouble