list 返回列表的总和：错误：参数的“类型”（列表）无效
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Sum of returned list: Error: invalid 'type' (list) of argument
提问by Bas
For my script I'm returning a bunch of variables in R, and after splitting up my script in more functions I need to return some lists, along with other data.
对于我的脚本，我在 R 中返回了一堆变量，在将脚本拆分为更多函数之后，我需要返回一些列表以及其他数据。
I know I can return multiple values by c(value1, value2). But how can I do this when one of the items returned is actually a list?
I'm returning listOne, however it looks like the data type gets changed when returning.
How can I get return the list without changing its type?
我知道我可以通过c(value1, value2). 但是，当返回的项目之一实际上是列表时，我该怎么做？我正在返回 listOne，但是看起来返回时数据类型已更改。如何在不更改列表类型的情况下返回列表？
Here's an example:
下面是一个例子：
B <- function(){
listOne <- c(1,2,3,4,5,6)
testString <- "Test"
return(list(listOne, testString))
}
returnlist <- B()
Assigning the variables according to the returned list:
根据返回的列表分配变量：
copy.listOne <- returnlist# [1]
copy.testString <- returnlist[2]
Expected output:
预期输出：
listOne <- c(1,2,3,4,5,6)
print(sum(listOne))
# [1] 21
Actual output:
实际输出：
print(sum(copy.listOne))
Error in print(sum(copy.listOne)) :
error in evaluating the argument 'x' in selecting a method for function 'print': Error in sum(copy.listOne) : invalid 'type' (list) of argument
回答by LyzandeR
When you are working with lists you need to use [[in order to subset them. In your case when you create the function as follows
当您使用列表时，您需要使用[[它来对它们进行子集化。在您创建函数时的情况如下
B <- function(){
listOne <- c(1,2,3,4,5,6)
testString <- "Test"
return(list(listOne, testString))
}
returnlist <- B()
you then need to use [[in order to access the elements of that list.
然后您需要使用[[以访问该列表的元素。
As you can see below all work now properly:
正如您在下面看到的那样，现在所有工作都正常：
> returnlist[[1]]
[1] 1 2 3 4 5 6
> returnlist[[2]]
[1] "Test"
> sum(returnlist[[1]])
[1] 21
