Randomly generate pairs from a table of pairwise weights.

ptable.clj

(require [clojure.test.check.generators :as gen])

(defn ptable
  [label cols & rows]
  (let [ncols (count cols)]
    (assert (= 0 (mod (count rows) (inc ncols))))
    (mapcat
     (fn [[r & vs]]
       (map (fn [c v] [v [c r]]) cols vs))
     (partition (inc ncols) rows))))

(defn generator
  [table]
  (gen/frequency
   (map #(update % 1 gen/return) table)))

(->
  (ptable
   :_       [:srcA   :srcB   :srcC]
   :dest1      90      15        5
   :dest2      15      40       10
   :dest3      15      15       90)
  generator
  (gen/sample 500))