do.call()不喜欢基函数"c".有清单 [英] do.call() doesn't like base function "c" with a list

问题描述

我有一段较大的代码，但是我已经将问题缩小到了- 所以我想返回一个串联列表.

I have a larger section of code but I've narrowed down the problem to this - So I want to return a concatenated list.

do.call(c,"X")
Error in do.call(c, "X") : second argument must be a list

因此，在上面它抱怨SECOND参数不是列表.

So above it complains about the SECOND argument not being a list.

asimplelist=list(2,3,4)
class(asimplelist)
[1] "list"
do.call(c,asimplelist)
Error in do.call(c, asimplelist) : 
'what' must be a function or character string

为什么不返回串联列表? C是合法函数，并且正在传递一个列表?

Why will this not return a concatenated list ? C is a legit function, and it's being passed a list?

args(do.call)
function (what, args, quote = FALSE, envir = parent.frame()) 
NULL 

所以"what"是它抱怨的函数参数.

So "what" is the function argument it is complaining about.

推荐答案

我将从尼克·肯尼迪:

最好将c用双引号引起来.

It might be better to put the c in double quotes.

如果用户在全局环境中具有名为c的非功能，则do.call(c, dates)将失败，并显示错误"Error in do.call(c, list(1:3)) : 'what' must be a character string or a function".

If the user has a non-function named c in the global environment, do.call(c, dates) will fail with the error "Error in do.call(c, list(1:3)) : 'what' must be a character string or a function".

很显然，定义c可能不是最佳实践，但是人们通常习惯做a <- 1; b <- 2; c <- 3.

Clearly it may not be best practice to define c, but it's quite common for people to do a <- 1; b <- 2; c <- 3.

在大多数情况下，R在这种情况下仍然可以正常工作； c(1, 2)仍然可以工作，但do.call(c, x)无效.

For most purposes, R still works fine in this scenario; c(1, 2) will still work, but do.call(c, x) won't.

当然，如果用户已将c重新定义为功能(例如c <- sum)，则do.call将使用重新定义的功能.

Of course if the user has redefined c to be a function (e.g. c <- sum), then do.call will use the redefined function.

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