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