[Rd] [[ vs. .subset2

[Spencer Graves]

Dear Gabor: 

      Does the following answer your question: 

 > tst <- list(a=1, b=2)
 > tst[numeric(0)]
list()
 > tst[[numeric(0)]]
Error in tst[[numeric(0)]] : attempt to select less than one element

      Spencer

Gabor Grothendieck wrote:
> In the code below test2() gives an error message:
>
>    Error in .subset2(x, i, exact = exact) :
>      attempt to select less than one element
>
> even though test(), which is nearly the same, gives
> the expected result.  BOD is a data set that comes
> with R.   Is this a bug?
>
>
> idx <- 2
>
> # returns expected result
> test <- function(pf = parent.frame()) .subset2(BOD, pf$idx)
> test()
>
> # gives error message !!!
> test2 <- function(pf = parent.frame()) BOD[[pf$idx]]
> test2()
>
>
> I tried this on Windows Vista under:
>
>   
>> R.version.string
>>     
> [1] "R version 2.7.1 RC (2008-06-16 r45949)"
>
> and
>
>   
>> R.version.string
>>     
> [1] "R version 2.8.0 Under development (unstable) (2008-06-28 r46012)"
>
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