[英]Clojure - Using Filters
我正在尝试遍历地图以计算单个事件的特定发生次数,尽管在使用以下过滤器时遇到了一些麻烦。 我想要做的是过滤并计算每个“ ORDER_CATEGORY”的特定实例,这些实例以多个级别(1、2等)出现。 我可以遍历月份并进行打印,但可以过滤并计算ORDER_CATEGORY的计数,这似乎对我不起作用。
GROUPED_BY_MONTH(group-by :MONTH CON)
ALL (for [flop GROUPED_BY_MONTH] {
:MONTH (:MONTH (first (second flop)))
:ORDER1 (count (filter #(= "1" (:ORDER_CATEGORY %)) flop))
:ORDER2 (count (filter #(= "2" (:ORDER_CATEGORY %)) flop))
})
我正在处理XML文件,这些文件已成功地管理到一个串联列表中,并按以下方式分组:
[“ 01” [{:MONTH“ 01”,:ORDER_CATEGORY“ 1”} {:MONTH“ 01”,:ORDER_CATEGORY“ 1”} {:MONTH“ 01”,:ORDER_CATEGORY“ 2”}]] [“ 02” [{:MONTH“ 02”,:ORDER_CATEGORY“ 1”} {:MONTH“ 02”,:ORDER_CATEGORY“ 2”} {:MONTH“ 02”,:ORDER_CATEGORY“ 2”}]]
因此,我希望有:
MONTH ORDER1 ORDER2
01 -------- 2 -------------- 1
02 -------- 1 -------------- 2
这可能是我忽略的相对简单的修复程序,因此感谢您的提前帮助!
我首先将数据转换为:
user=> (pprint x)
[{:MONTH "01", :ORDER_CATEGORY "1"}
{:MONTH "01", :ORDER_CATEGORY "1"}
{:MONTH "01", :ORDER_CATEGORY "2"}
{:MONTH "02", :ORDER_CATEGORY "1"}]
并使用功能:
user=> (defn inc1 [x] (if x (inc x) 1))
user=> (reduce (fn [acc {:keys [MONTH ORDER_CATEGORY]}]
(update-in acc [[MONTH ORDER_CATEGORY]] inc1)) {} x)
{["02" "1"] 1, ["01" "2"] 1, ["01" "1"] 2}
关键是[月份类别],值是订单数。
您的for循环不起作用,因为您已将这样的映射项绑定到flop
["01" [{:MONTH "01", :ORDER_CATEGORY "1"} ...]]
您的过滤器表达式会将其作为输入:
(filter #(= "1" (:ORDER_CATEGORY %)) flop)
这将不起作用,因为:ORDER_CATEGORY
都不会返回sth。 表示"01"
,也不表示序列[{:MONTH ...} ...]
。
鉴于绑定到flop
是MapEntry,可以使用val
来解决此问题:
(filter #(= "1" (:ORDER_CATEGORY %)) (val flop))
。
例如:
(for [flop GROUPED_BY_MONTH]
{:MONTH (:MONTH (first (second flop)))
:ORDER1 (count (filter #(= "1" (:ORDER_CATEGORY %)) (val flop)))
:ORDER2 (count (filter #(= "2" (:ORDER_CATEGORY %)) (val flop)))})
=> ({:MONTH "01", :ORDER1 2, :ORDER2 1} {:MONTH "02", :ORDER1 1, :ORDER2 0})
您还可以使用析构函数使代码更清晰:
(for [[month maps] GROUPED_BY_MONTH]
{:MONTH month
:ORDER1 (count (filter #(= "1" (:ORDER_CATEGORY %)) maps))
:ORDER2 (count (filter #(= "2" (:ORDER_CATEGORY %)) maps))})
=> ({:MONTH "01", :ORDER1 2, :ORDER2 1} {:MONTH "02", :ORDER1 1, :ORDER2 0})
请注意,通常,此解决方案更有利:
(reduce (fn [acc {:keys [MONTH ORDER_CATEGORY]}]
(update-in acc [MONTH ORDER_CATEGORY]
(fnil inc 0)))
{} CON)
=> {"02" {"1" 1}, "01" {"2" 1, "1" 2}}
它返回一个month->order-category->count
映射,该映射独立于输入集中存在的订单类别和月份的种类和类型。
例如
(reduce (fn [acc {:keys [MONTH ORDER_CATEGORY]}]
(update-in acc [MONTH ORDER_CATEGORY]
(fnil inc 0)))
{} (conj CON
{:MONTH "01" :ORDER_CATEGORY "foo"}
{:MONTH "02" :ORDER_CATEGORY "foo"}
{:MONTH "02" :ORDER_CATEGORY "bar"}
{:MONTH "02" :ORDER_CATEGORY "1"}))
=> {"02" {"bar" 1, "foo" 1, "1" 2}, "01" {"foo" 1, "2" 1, "1" 2}}
但是,您应该知道,如果ORDER_CATEGORY
的计数为0,则结果中没有任何关联的值。
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