Clojure 学习入门（12）—— map/pmap

clojure map数据结构的常用方法，小结一下

map 各种排序

(println (sorted-map-by > 1 "a", 2 "b", 3 "c"))     ;; {3 c, 2 b, 1 a};; 相等 value 取一个(let [results {:A 1 :B 2 :C 2 :D 5 :E 1 :F 1}]  (println (into (sorted-map-by (fn [key1 key2]                                  (compare (get results key2)                                           (get results key1))))                 results)))              ;;    {:D 5, :C 2, :A 1};; 全不等 value (let [results {:A 1 :B 2 :F 4 :E 3 :D 6 :C 5}]  (println (into (sorted-map-by (fn [key1 key2]                                  (compare (get results key2)                                           (get results key1))))                 results)))              ;;    {:D 6, :C 5, :F 4, :E 3, :B 2, :A 1};; value 升序(let [results {:A 1 :B 2 :F 4 :E 3 :D 6 :C 5}]  (println (into (sorted-map-by (fn [key1 key2]                                  (compare [(get results key1) key1]                                           [(get results key2) key2])))                 results)))    ;;   {:A 1, :B 2, :E 3, :F 4, :C 5, :D 6};; value 降序(let [results {:A 1 :B 2 :F 4 :E 3 :D 6 :C 5}]  (println (into (sorted-map-by (fn [key1 key2]                                  (compare [(get results key2) key2]                                           [(get results key1) key1])))                 results)))    ;;   {:D 6, :C 5, :F 4, :E 3, :B 2, :A 1};; value 升序(let [results {:A 1 :B 2 :F 4 :E 3 :D 6 :C 5}]  (println (into (sorted-map-by (fn [key1 key2]                                  (compare [(get results :key1) key1]                                           [(get results :key2) key2])))                 results)))    ;;   {:A 1, :B 2, :C 5, :D 6, :E 3, :F 4};; value 降序(let [results {:A 1 :B 2 :F 4 :E 3 :D 6 :C 5}]  (println (into (sorted-map-by (fn [key1 key2]                                  (compare [(get results :key2) key2]                                           [(get results :key1) key1])))                 results)))    ;;   {:F 4, :E 3, :D 6, :C 5, :B 2, :A 1};; 默认升序排列(println (into (sorted-map) {:2013-12-23 0, :2013-12-22 0, :2013-12-21 0, :2013-12-20 3600, :2013-12-24 0, :2013-12-18 0, :2013-12-19 3600}));; {:2013-12-18 0, :2013-12-19 3600, :2013-12-20 3600, :2013-12-21 0, :2013-12-22 0, :2013-12-23 0, :2013-12-24 0};; 取排序后最末一个(println (last (into (sorted-map) {:2013-12-23 0, :2013-12-22 0, :2013-12-21 0, :2013-12-20 3600, :2013-12-24 0, :2013-12-18 0, :2013-12-19 3600})));; [:2013-12-24 0];; 自定义key降序排序(let [results {:2013-12-23 0, :2013-12-22 0, :2013-12-21 0, :2013-12-20 3600, :2013-12-24 0, :2013-12-18 0, :2013-12-19 3600}]  (println (into (sorted-map-by (fn [key1 key2]                                  (compare [(get results :key2) key2]                                           [(get results :key1) key1])))                 results)))    ;; {:2013-12-24 0, :2013-12-23 0, :2013-12-22 0, :2013-12-21 0, :2013-12-20 3600, :2013-12-19 3600, :2013-12-18 0}

先排序后取值

;; 先对日期排序，然后取前num天(defn take-sort-data [data num]    (let [          result-sorted  (into (sorted-map-by (fn [key1 key2]                                                (compare [(get data :key2) key2]                                                         [(get data :key1) key1]))) data)    ;; 对日期排序          result (select-keys result-sorted (take num (keys result-sorted)))]      (println "data = " data)      (println "result-sorted = " result-sorted)      (println "result = " result)      (println "json/write-str result = " (json/write-str result)))    )(let [data {:2013-12-23 0, :2013-12-22 0, :2013-12-21 0, :2013-12-20 3600, :2013-12-24 0, :2013-12-18 0, :2013-12-19 3600}]  (take-sort-data  data 6)  (take-sort-data  data 4)  );; (take-sort-data  data 6) 's result;data =  {:2013-12-24 0, :2013-12-23 0, :2013-12-20 3600, :2013-12-21 0, :2013-12-22 0, :2013-12-18 0, :2013-12-19 3600};result-sorted =  {:2013-12-24 0, :2013-12-23 0, :2013-12-22 0, :2013-12-21 0, :2013-12-20 3600, :2013-12-19 3600, :2013-12-18 0};result =  {:2013-12-19 3600, :2013-12-20 3600, :2013-12-21 0, :2013-12-22 0, :2013-12-23 0, :2013-12-24 0};json/write-str result =  {"2013-12-19":3600,"2013-12-20":3600,"2013-12-21":0,"2013-12-22":0,"2013-12-23":0,"2013-12-24":0};;; (take-sort-data  data 4) 's result;data =  {:2013-12-24 0, :2013-12-23 0, :2013-12-20 3600, :2013-12-21 0, :2013-12-22 0, :2013-12-18 0, :2013-12-19 3600};result-sorted =  {:2013-12-24 0, :2013-12-23 0, :2013-12-22 0, :2013-12-21 0, :2013-12-20 3600, :2013-12-19 3600, :2013-12-18 0};result =  {:2013-12-21 0, :2013-12-22 0, :2013-12-23 0, :2013-12-24 0};json/write-str result =  {"2013-12-21":0,"2013-12-22":0,"2013-12-23":0,"2013-12-24":0}

参考推荐：

sorted-map

sorted-map-by

compare