[Rd] NextMethod ignoring changed argument

Uwe Ligges
Wed, 27 Oct 2004 08:56:37 -0000

Gabor Grothendieck wrote:

>
> Is this a bug?  We define the [ operator for class test.
> All it does is force drop to be FALSE and then calls
> the NextMethod.  If we specify drop= in the call then
> it works as expected (### 2 and ### 3) but if we do not
> specify drop (### 1) then it acts as if drop=TRUE
> even though we have set it to FALSE within [.test .
>
>
>>"[.test" <- function(x, i, j, drop = TRUE) {
>
> + drop <- FALSE
> + NextMethod("[")
> + }
>
>>x <- structure(matrix(1:12, 4, 3), class = "test")
>
>
>>x[1,]  ### 1 - why does it ignore drop=FALSE in [.test ????
>
> [1] 1 5 9
>
>
>>x[1,,drop = TRUE]  ### 2 - ok
>
>      [,1] [,2] [,3]
> [1,]    1    5    9
>
>>x[1,,drop = FALSE]  ### 3 - ok
>
>      [,1] [,2] [,3]
> [1,]    1    5    9
>
>>R.version.string # windows XP
>
> [1] "R version 2.0.0, 2004-10-04"
>


Well, the *arguments* of the encolsing function are taken, but not the
objects defined therein. What you can do is:

"[.test" <- function(x, i, j, drop = TRUE) {
     NextMethod("[", drop = FALSE)
}

Uwe Ligges