Question

我已:

(def data [[1 3 4 7 9] [7 6 3 2 7] [1 9 8 6 2]])

我想要平均这些(需要满足以下条件):

[3 6 5 5 6]

和MATLAB一样:

mean([1 3 4 7 9; 7 6 3 2 7; 1 9 8 6 2])

With Incan 我可以做到:

(map #(/ % (count m)) (apply plus data))

If data is rather large (and I have lots of them) is there a better way to do this?
Does it help to calculate the (count m) beforehand?
Does it help to defn the #(/ % (count m)) beforehand?

Answer 1

在不知道如何使用任何扫描器的情况下,你可以“从零开始”这样做。

(let [data [[1 3 4 7 9] [7 6 3 2 7] [1 9 8 6 2]]
      num (count data)]
  (apply map (fn [& items]
               (/ (apply + items) num))
         data))

;=> (3 6 5 5 6)

Answer 2

这里简单易行:

(def data [[1 3 4 7 9] [7 6 3 2 7] [1 9 8 6 2]])

(defn average [coll] 
  (/ (reduce + coll) (count coll)))

(defn transpose [coll]
   (apply map vector coll))

(map average (transpose data))
=> (3 6 5 5 6)

Answer 3

截至2013年,我的建议是只使用分。进口这一功能:

(mean [[1 3 4 7 9] [7 6 3 2 7] [1 9 8 6 2]])
=> [3.0 6.0 5.0 5.0 6.0]

core.matrix.stats builds on the core.matrix API, so it will also work on other more optimised implementations of vectors and matrices - this is likely to be a better option if you are doing a lot of heavy matrix processing.

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