enumerated-distribution-gen.clj

(defn enumerated-distribution-gen
  "Create a random generator producing weighted inputs
   - Input: a sequence of pairs [value weight-of-value]
   - Output: a random generator that picks values from the input
     such that P(value) = Weight(value) / Sum(all weights)"
  [enum-dist]
  {:pre [(pos? (count enum-dist))]}
  (if (= 1 (count enum-dist))
    (constantly (ffirst enum-dist))
    (let [buckets (enum-dist->buckets enum-dist)]
      (fn []
        (let [[v1 v2 p] (rand-nth buckets)]
          (if (< (rand) p) v1 v2))))))