我想这个问题可以作为入门级的clojure问题.我基本上有多次麻烦地处理一个clojure地图并提取不同类型的数据.
给定这样的映射,我试图基于多个嵌套键来计算条目：
[
{
"a": "X","b": "M","c": 188
},{
"a": "Y","c": 165
},"c": 313
},"b": "P","c": 188
}
]
首先,我想通过a键值对条目进行分组：
{
"X" : [
{
"b": "M","c": 188
}
],"Y" : [
{
"b": "M","c": 165
},{
"b": "M","c": 313
},{
"b": "P","c": 188
}
]
}
其次,我想假设b键的值是重复的,并忽略其余的键：
{
"X" : [
{
"b": "M"
}
],"Y" : [
{
"b": "M"
}
{
"b": "P"
}
]
}
然后,只需计算b键的所有实例：
{
"X" : 1,"Y" : 2
}
当我通过monger获取数据时,我定义了：
(defn db-query
([coll-name]
(with-open [conn (mg/connect)]
(doall (mc/find-maps (mg/get-db conn db-name) coll-name))))
然后点击路障：
(defn get-sums [request]
(->> (db-query "data")
(group-by :a)
(into {})
keys))
我怎么能从这里继续？
解决方法
这是一种天真的方法,我相信有更好的方法,但它可能是你需要弄清楚的.
(into {}
(map
; f
(fn [ [k vs] ] ;[k `unique count`]
[k (count (into #{} (map #(get % "b") vs)))])
; coll
(group-by #(get % "a") DATA))) ; "a"s as keys
;user=> {"X" 1,"Y" 2}
说明：
; I am using your literal data as DATA,just removed the,and ;
(def DATA [{...
(group-by #(get % "a") DATA) ; groups by "a" as keys
; so I get a map {"X":[{},...] "Y":[{},{},...]}
; then I map over each [k v] pair where
; k is the map key and
; vs are the grouped maps in a vector
(fn [ [k vs] ]
; here `k` is e.g. "Y" and `vs` are the maps {a _,b,_,c _}
; now `(map #(get % "b") vs)` gets me all the b values
; `into set` makes them uniqe
; `count` counts them
; finally I return a vector with the same name `k`,; but the value is the counted `b`s
[k (count (into #{} (map #(get % "b") vs)))])
; at the end I just put the result `[ ["Y" 2] ["X" 1] ]` `into` a map {}
; so you get a map
