具有动态尺寸的数组子集部分 [英] Subset parts of array with dynamic dimension

问题描述

我想对维数为k的动态数组进行子集化.

I would like to subset an array with a dynamic number of dimensions k.

以示例为例:

A <- array(1:3^4, dim=c(3,3,3,3))

由于尺寸可以变化(此处未显示)，因此我不能简单地定义a，b，c，d并通过进行查询

Because the dimensions can vary (not shown here), I cannot simply define a, b, c, d and make the query via

a <- 1:2; b <- 2; c <- 2:3; d = 1
A[a, b, c, d]

此处已显示，如果仅想对进行子集化单个元素，就可以这样处理:

Here has been shown that if one would like to subset only a single element, one can go about it like this:

e <- 1; f <- 2; g <- 3; h <- 1
A[matrix(c(e, f, g, h), nrow = 1)]

这可以使维数保持灵活，但是我只能对单个元素进行子集化，因为我无法在矩阵中表示序列a，b，c，d.

This allows me to keep the number of dimensions flexible, but I can only subset single elements, because I cannot represent the sequences a, b, c, d in a matrix.

理想的情况是我可以得到

The desired situation is that I can get the output of

A[a, b, c, d]

不对尺寸进行硬编码，即通过以下方式访问数组

without hardcoding the dimensions, i.e. access the array via

A[object]

问题基本上是可能的，如果是，对象"的外观如何.

and the question is basically is this possible and if yes how does 'object' look like.

任何帮助将不胜感激！

推荐答案

如果将 object 定义为列表，则可以使用 do.call 将该列表用作子功能 ["的参数.如果将数组作为列表中的第一项包括在内，则可以直接调用 [":

If you define object as a list, you can use do.call to use that list as parameters for the subsetting function [. If you include the array as the first item in the list, you can call [ directly:

object <- list(A, a, b, c, d)

do.call(`[`, object)
##      [,1] [,2]
## [1,]   13   22
## [2,]   14   23

如果您不希望包含数组(如果您有很多这样的对象并且数组很大，则将需要大量的内存)，则可以编写一个匿名函数，仅使用子集参数，不是什么是子集:

If you don't want to include the array (if you have lots of these objects and the array is large, it will require a lot of memory), you can write an anonymous function to just use just the subsetting parameters, not what's being subset:

object <- list(a, b, c, d)

do.call(function(...){A[...]}, object)
##      [,1] [,2]
## [1,]   13   22
## [2,]   14   23

这实际上是 abind :: asub 采用的确切方法:

That is actually the exact approach abind::asub takes:

object <- list(a, b, c, d)

abind::asub(A, object)
##      [,1] [,2]
## [1,]   13   22
## [2,]   14   23

请注意，此处的参数匹配是关系型的，因此，如果其中一个为空，则需要包含 NULL :

Note that parameter matching here is relational, so if one is empty, it will need to contain NULL:

object <- list(NULL, b, c, d)

abind::asub(A, object)
##      [,1] [,2]
## [1,]   13   22
## [2,]   14   23
## [3,]   15   24

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