tasks a-s

Task/Probabilistic-choice/Clojure/probabilistic-choice.clj

@@ -0,0 +1,22 @@
+(defn to-cdf [pdf]
+  (reduce
+    (fn [acc n] (conj acc (+ (or (last acc) 0) n)))
+    []
+    pdf))
+
+(defn choose [cdf]
+  (let [r (rand)]
+    (count
+      (filter (partial > r) cdf))))
+
+(def *names* '[aleph beth gimel daleth he waw zayin heth])
+(def *pdf* (map double [1/5 1/6 1/7 1/8 1/9 1/10 1/11 1759/27720]))
+
+(let [num-trials 1000000
+      cdf (to-cdf *pdf*)
+      indexes (range (count *names*)) ;; use integer key internally, not name
+      expected (into (sorted-map) (zipmap indexes *pdf*))
+      actual (frequencies (repeatedly num-trials #(choose cdf)))]
+  (doseq [[idx exp] expected]
+    (println "Expected number of" (*names* idx) "was"
+             (* num-trials exp) "and actually got" (actual idx))))