子集3维数组时，请不要丢弃维 [英] Don't drop dimensions when subseting 3-dimensional array

问题描述

让 A 是一个 1 x 2 x 2 数组:

> A <- array(0, dim=c(1,2,2))
> A
, , 1

     [,1] [,2]
[1,]    0    0

, , 2

     [,1] [,2]
[1,]    0    0

然后 A [,, 1] 是无量纲的:

> A[,,1]
[1] 0 0

我想要:

     [,1] [,2]
[1,]    0    0

drop 参数不能产生我想要的:

The drop argument does not yield what I want:

> A[,,1,drop=FALSE]
, , 1

     [,1] [,2]
[1,]    0    0

我觉得很烦.越野车，因为R将向量标识为列矩阵，而不是行矩阵.

I find that annoying. And buggy, because R identifies vectors to column matrices, not to row matrices.

我当然可以做 matrix(A [,, 1]，1，2).有没有更方便的方法?

Of course I could do matrix(A[,,1], 1, 2). Is there a more convenient way?

推荐答案

我们可以根据提取的 MARGIN 分配 dim

We can just assign the dim based on the MARGIN we are extracting

`dim<-`(A[, ,1], apply(A, 3, dim)[,1])
 #     [,1] [,2]
 #[1,]    0    0

使用另一个示例

B <- array(0, dim = c(2, 1, 2))
`dim<-`(B[, ,1], apply(B, 3, dim)[,1])
 #    [,1]
#[1,]    0
#[2,]    0

---

如果我们使用的是打包解决方案，那么 abind 中的 adrop 可能会获得预期的输出

---

If we are using a package solution, then adrop from abind could get the expected output

library(abind)
adrop(A[,,1,drop=FALSE], drop = 3)
#      [,1] [,2]
# [1,]    0    0

adrop(B[,,1,drop=FALSE], drop = 3)
#     [,1]
#[1,]    0
#[2,]    0

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