[Rd] Lists and data frames (PR#8143)

[Gavin Simpson]

On Mon, 2005-09-19 at 15:34 +0200, fwagner at fh-lausitz.de wrote:
> Full_Name: Frank Wagner
> Version: R 2.1.1
> OS: Windows
> Submission from: (NULL) (193.174.73.34)
> 
> 
> Hi,
> The pdf file R-intro descripe on page 27 that lists can be extended by adding
> numbers.
> Unfortunately, it's not working 
> ## example :
> 
> # if i did not declare the variable an error occurs : object not found
> mylist <- list() 
> mylist[1] <- list(value1=3, value2=5)
> ## Error

You need to use [[x]] to subset a list:

> mylist <- list()
> mylist[[1]] <- list(value1=3, value2=5)
> mylist
[[1]]
[[1]]$value1
[1] 3

[[1]]$value2
[1] 5

> str(mylist)
List of 1
 $ :List of 2
  ..$ value1: num 3
  ..$ value2: num 5

I don't know whether there is a typo on page 27 or not: [x] is valid, it
just means something different to [[x]] - as explained on page 26 of
said manual. If it was intentional, then IMHO it is not the most clear
example of extending a list - the [[x]] notation is what I would expect
to have to use - after reading page 26 of course...

HTH

G
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Gavin Simpson                     [T] +44 (0)20 7679 5522
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