Clojure：对地图集合中的值求和 [英] Clojure: summing values in a collection of maps

问题描述

我试图通过它们的公共密钥对地图集合的值进行求和。我有这个代码片段：

I am trying to sum up values of a collection of maps by their common keys. I have this snippet:

(def data [{:a 1 :b 2 :c 3} {:a 1 :b 2 :c 3}]
(for [xs data] (map xs [:a :b]))
((1 2) (1 2))

Final result should be ==> (2 4)

基本上，

我现在的问题是如何总结这些值？我试图使用reduce但是

My question now is how can I now sum up those values? I tried to use "reduce" but it works only over sequences, not over collections.

感谢。

=== EDIT ====

===EDIT====

使用Joost的建议我出来了：

Using the suggestion from Joost I came out with this:

(apply merge-with + (for [x data] (select-keys x [:col0 :col1 :col2]))

b $ b

这会迭代一个集合并对选择的键求和。我添加的select-keys部分是特别需要避免的麻烦，当集合中的地图包含文字，而不仅仅是数字。 p>

This iterates a collection and sums on the chosen keys. The "select-keys" part I added is needed especially to avoid to get in trouble when the maps in the collection contain literals and not only numbers.

推荐答案

如果你真的想对通用键的值求和，可以一步完成整个转换：

If you really want to sum the values of the common keys you can do the whole transformation in one step:

(apply merge-with + data)
=> {:a 2, :b 4, :c 6}

(apply map + '((1 2) (1 2)))
=> (2 4)

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