PigPen是Clojure的Map-Reduce，可以编译到ApachePig或者Cascading。
代码：
(require '[pigpen.core :as pig])(defn word-count [lines] (->> lines (pig/mapcat #(-> % first (clojure.string/lower-case) (clojure.string/replace #"[^\w\s]" "") (clojure.string/split #"\s+"))) (pig/group-by identity) (pig/map (fn [[word occurrences]] [word (count occurrences)]))))
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