Clojure:频率图的惯用代码

Question

让我们制作频率图:

(reduce #(update-in %1 [%2] (fnil inc 0)) {} ["a" "b" "a" "c" "c" "a"])

我担心的是lambda中的表达#(...)- 这是规范的方式吗？我能做得更好/更短吗？

编辑:我发现的另一种方式:

(reduce #(assoc %1 %2 (inc %1 %2 0)) {} ["a" "b" "a" "c" "c" "a"])

看似非常相似,有什么利弊？性能？

Answer 1

从Clojure 1.2开始,有一个frequencies功能clojure.core:

user=> (doc frequencies)
-------------------------
clojure.core/frequencies
([coll])
  Returns a map from distinct items in coll to the number of times
  they appear.

例:

user=> (frequencies ["a" "b" "a" "c" "c" "a"])
{"a" 3, "b" 1, "c" 2}

它碰巧使用瞬态和三元get; 看看(source frequencies)代码,它是高度的性能感知时的惯用语.