在Clojure中就地更新矩阵 [英] Update matrix in-place in Clojure

问题描述

假设我有一个Clojure矩阵 A 这样（为清楚起见，格式化）

Suppose I have a Clojure matrix A as such (formatted for clarity)

[[1 4 3]
 [1 7 3]
 [1 8 3]]

现在假设我要更新第一列的位置，通过eg将其乘以因子2，使得新矩阵变为

Now suppose I want to update the first column in place, by e.g. multiplying it by a factor of two, so that the new matrix becomes

[[2 4 3]
 [2 2 3]
 [2 8 3]]

如何在clojure中这样做？我已经尝试过 assoc 和像

How would one do this in clojure? I have tried things like assoc and stuff like

（slice A 1 0）2）（select A [0 1 2] [2 3]））

自然不行。如果有像 assoc 的矩阵例如

Naturally that did not work. It would be great if there was something like assoc for matrices e.g.

(massoc A [rows] [columns] replacement-vector)

c> numpy 在Python中：

or something simple like numpy in Python:

A[:,0]*2 = [[2 4 3]
            [2 2 3]
            [2 8 3]]

感谢

推荐答案

您应该查看 clojure.core / matrix ，看看它是否支持这样的操作。

You should look into clojure.core/matrix and see if it supports operations like this.

这里可能是你正在寻找的东西。将 assoc 更改为新值而不是在应用函数后更新应该很简单。

Here is something that may be what you're looking for. It should be trivial to change this to assoc a new value rather than updating after applying a function.

(defn mupdate-in
  "Update all `coll' rows at `column' with `f'"
  [coll column f & args]
  (reduce #(apply update-in %1 [%2 column] f args)
          coll
          (range (count coll))))

例如：

(def m [[1 4 3]
        [1 7 3]
        [1 8 3]])

(mupdate-in m 0 * 2)
;; [[2 4 3]
;;  [2 7 3]
;;  [2 8 3]]

(mupdate-in m 2 + 10)
;; [[1 4 13]
;;  [1 7 13]
;;  [1 8 13]]

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