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

[Uwe Ligges]

Gavin Simpson wrote:

> 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


This is a list of a list, but that is not the same as the stuff we are 
discussing here. See below.


> 
>>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...

Folks, please specify which version of the manual you are speaking 
about, e.g. by giving a chapter's/section's name.

The statement on what is referred to page 27 in this thread is completly 
correct.

Note that a list is nothing else than a vector of mode list which 
contains in each element a list of length one.

Hence you *can* say
mylist[1:2] <- list(value1=3, value2=5)
or
c(mylist, list(value1=3, value2=5))
or whatever.


Uwe Ligges



> HTH
> 
> G