r 以编程方式确定的维度的数组切片 [英] r array-slice of programmatically determined dimension

问题描述

有没有一种方法可以在 R 中优雅地指定多维数组中的切片，从而事先不知道维数?

Is there a way of elegantly specify a slice in a multidimensional array in R, whereby the number of dimensions is not known beforehand?

例如，对于 5 维数组，可以使用

For instance, for a 5-dimensional array, slicing out the last dimension can be done using

fourdimslice <- fivedimarray[,,,,1]

但我想为任意维度编写代码，例如

but I'l like to code this for arbitrary dimensions, something like

slice <- arbitrarydimarray(dim=5, index=1)

我一直无法理解 do.call('[', ...) 是否是一种方法.我也试过命名维度，但 a[fifth=1] 没有按照我想要的方式解释.

I've not been able to understand if do.call('[', ...) would be an approach. I've also tried named dimensions, but a[fifth=1] is not interpreted the way I would want here.

我想像 apply() 这样的函数需要做类似的事情.

I suppose functions like apply() need to do similar things.

推荐答案

您可以使用 asub，来自 abind 包.

You can use asub, from the abind package.

# Sample data: a 5-dimensional array
x <- array(seq_len(prod(2:6)), dim=2:6)

library(abind)
str( asub(x, 1, 5) )
# int [1:2, 1:3, 1:4, 1:5] 1 2 3 4 5 6 7 8 9 10 ...
str( x[,,,,1] )
# int [1:2, 1:3, 1:4, 1:5] 1 2 3 4 5 6 7 8 9 10 ...
all( asub(x, 1, 5) == x[,,,,1] )
# [1] TRUE

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