How do I calculate a Poisson number in Scala

Question

There is no standard library function to do this. How can I do it efficiently?

score 3 · Answer 1 · answered Apr 22 '13 at 21:48

3

Scala Breeze, http://www.scalanlp.org/ has a Poisson class in its stats.distributions package.

case class Poisson(mean: Double)(implicit rand: RandBasis = Rand)

answered Apr 22 '13 at 21:48

Keith Pinson

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score 0 · Answer 2 · edited May 23 '17 at 12:04

0

I translated this answer to Scala:

def recursive_poisson_helper(m:Long, r:Long, p:Double, i:Long):Double = {
  if (r == i) {
    p
  } else {
    recursive_poisson_helper(m, r, (p * m) / (i + 1), i + 1)
  }
}

def efficient_poisson(m:Long, r:Long): Double = {
  val p = math.exp(-m)
  recursive_poisson_helper(m, r, p, 0)
}

edited May 23 '17 at 12:04

Community

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answered Apr 22 '13 at 20:03

Moishe Lettvin

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`i` should probably be a `Long` as well otherwise you shouldn’t really test for equality. – Debilski Apr 22 '13 at 21:24
And the function names don't follow Scalas style guide, there are all these unnecessary curly braces and `recursive_poisson_helper` should be a inner function. – kiritsuku Apr 22 '13 at 21:39

How do I calculate a Poisson number in Scala

2 Answers2