有没有clojure函数来“加入”两个地图列表? [英] Is there a clojure function to "join" two list of maps?
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问题描述
我正在寻找一个连接函数,就像加入sql,例如:
这里是两个地图列表:
(def a [{:user_id 1:nameuser 1}
/ pre>
{:user_id 2:nameuser 2}])
(def b [{:user_id 2:emaile 2}
{:user_id 1:emaile 1}])
我想在user_id上加入a和b:
[{:user_id 1:nameuser 1:emaile 1}
{:user_id 2:nameuser 2:emaile 2}]
在clojure或其他库中可以实现这个功能吗?
解决方案clojure.set / join 会做这件事。
(使用'clojure.set)
(clojure.set / join a b); => #{{:emaile 1,:nameuser 1,:user_id 1} {:emaile 2,:nameuser 2,:user_id 2}}
不提供第三个参数,函数将在所有公共键上加入:
(def a [{:id1 1:id2 2:namen 1} {:id1 2:id2 3:namen 2}])
:id1 1:id2 2:urlu 1} {:id1 2:id2 4:urlu 2}])
(def c [{:id1 1:id2 2:urlu 1 } {:id1 2:urlu 2}]); :第二条记录中缺少id2
(clojure.set / join a b); #{{:namen 1,:urlu 1,:id1 1,:id2 2}}
(clojure.set / join a c); #{{:namen 2,:urlu 2,:id1 2,:id2 3} {:namen 1,:urlu 1,:id1 1,:id2 2}}
仅在id1上加入a和b:
(clojure.set / join ab {:id1:id1}); #{{:namen 2,:urlu 2,:id1 2,:id2 4} {:namen 1,:urlu 1,:id1 1,:id2 2}}
我们甚至可以通过不同的集合加入不同的集合:
(clojure.set / join ab {:id1:id2}); #{{:namen 2,:urlu 1,:id1 1,:id2 2}}
I am looking for a join function which is like join in sql,for example:
Here is two list of maps:
(def a [{:user_id 1 :name "user 1"} {:user_id 2 :name "user 2"}]) (def b [{:user_id 2 :email "e 2"} {:user_id 1 :email "e 1"}])
I want join a and b on user_id to get:
[{:user_id 1 :name "user 1" :email "e 1"} {:user_id 2 :name "user 2" :email "e 2"}]
Is there some function in clojure or other library which could achieve this?
解决方案clojure.set/join will do the thing.
(use 'clojure.set) (clojure.set/join a b) ; => #{{:email "e 1", :name "user 1", :user_id 1} {:email "e 2", :name "user 2", :user_id 2}}
Without providing 3rd argument, function will join on all common keys:
(def a [{:id1 1 :id2 2 :name "n 1"} {:id1 2 :id2 3 :name "n 2"}]) (def b [{:id1 1 :id2 2 :url "u 1"} {:id1 2 :id2 4 :url "u 2"}]) (def c [{:id1 1 :id2 2 :url "u 1"} {:id1 2 :url "u 2"}]) ; :id2 is missing in 2nd record (clojure.set/join a b) ; #{{:name "n 1", :url "u 1", :id1 1, :id2 2}} (clojure.set/join a c) ; #{{:name "n 2", :url "u 2", :id1 2, :id2 3} {:name "n 1", :url "u 1", :id1 1, :id2 2}}
To join a and b only on id1:
(clojure.set/join a b {:id1 :id1}) ; #{{:name "n 2", :url "u 2", :id1 2, :id2 4} {:name "n 1", :url "u 1", :id1 1, :id2 2}}
We can even join by different keys from different collections:
(clojure.set/join a b {:id1 :id2}) ; #{{:name "n 2", :url "u 1", :id1 1, :id2 2}}
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