如何在[子集中传递/使用字符串 [英] How to pass/use string in [ to subset

问题描述

如何将 [中的字符串传递/使用到子集，例如数组。我一直在考虑这样的事情（对于4个dims数组）：

How to pass/use string in [ to subset e.g. array. I've been thinking about something like this (for 4 dims array):

inputDims <- ",,'CCC',"

outputArray[parse(text=inputDims)]

以上没有行不通-如何实现？

Above doesn't work - how to achieve this?

我对在 [-如果可能的话，仅输入字符串（以示例中的形式表示）。

I am not interested in using logical vector (or matrix) inside [ - just string (in a form like it is in the example) if this is possible.

推荐答案

（这似乎是一个

使用<$ c $可能会弄清楚构建R函数调用所需的内容。 c>扫描创建适当长度的字符向量。然后将其附加到列表中，其中数组是第一个元素。需要将空位置转换为TRUE，以使切片成功：

Use scan to create a character vector of the proper length. Then append it into a list where the array is the first element. Need to convert the "empty" positions into TRUE, to get the slicing to succeed:

vec <- scan( text= inputDims, sep="," , what="")
arglist <- list(outputArray)
arglist[ 2:(length(vec)+1) ] <- as.list(vec)
arglist[ arglist==""] <- TRUE
# Using your example in the other question
> do.call("[", arglist )
   bb bbb
a1 NA  NA
a2 NA  NA
a3 NA  NA

您之前曾提到过abind :: asub，如果您想了解它对其参数进行的体操（与您的问题不太相似），那么使用加载的软件包执行以下操作：

You were earlier referred to abind::asub, and if you ant to see what gymnastics it does with its arguments (that are not sufficiently similar to your problem) then do this with the package loaded:

getAnywhere( asub.default )

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