Wolfgang Huber
2007-Jan-28 14:40 UTC
[Rd] "[", .local and S4 methods (was: "[" operator and indexing ambiguity)
Dear Tony, thanks for the tip with "nargs", when suitably applied, this answers the problem. The behaviour of "nargs" in S4 methods has some subtleties compared to that in normal functions, as shown in the example below. I admit that this is what had earlier created some confusion about the semantics of "nargs". From the perspective of "nargs" and its man page, this all seems fine, but its interaction with the S4 methods implementation was surprising to me and I'd be interested whether people think that this is the desired behaviour. ### ------------------- example code --------------------------- setClass("foo", representation(x="array")) a = new("foo") myfun = function (x, i, j, k, ..., drop=TRUE) { cat(paste(match.call()), "\nnargs()=", nargs(), missing(i), missing(j), missing(k), missing(drop), "\n\n") return(invisible(NULL)) } setMethod ("[", signature(x="foo", i="numeric", j="missing"), myfun) a[7] a[7,] myfun(a, 7) myfun(a, 7, ) showMethods("[", classes="foo", inc=TRUE) ### --------------------- example output ----------------------- .local x i j drop nargs()= 4 FALSE TRUE TRUE FALSE .local x i j drop nargs()= 4 FALSE TRUE TRUE FALSE ## here it seems impossible to distinguish a[7] from a[7,] ## also note that missing(drop) is FALSE myfun a 7 nargs()= 2 FALSE TRUE TRUE TRUE myfun a 7 nargs()= 3 FALSE TRUE TRUE TRUE Function: [ (package base) x="foo", i="numeric", j="missing" function (x, i, j, ..., drop = TRUE) { .local <- function (x, i, j, k, ..., drop = TRUE) { cat(paste(match.call()), "\nnargs()=", nargs(), missing(i), missing(j), missing(k), missing(drop), "\n\n") return(invisible(NULL)) } .local(x, i, j, ..., drop = drop) } ### ----------- example code 2 (different signature: no k) --- myfun = function (x, i, j, ..., drop=TRUE) { cat(paste(match.call()), "\nnargs()=", nargs(), missing(i), missing(j), missing(drop), "\n\n") return(invisible(NULL)) } setMethod ("[", signature(x="foo", i="numeric", j="missing"), myfun) a[7] a[7,] myfun(a, 7) myfun(a, 7, ) showMethods("[", classes="foo", inc=TRUE) ### --------------------- example output ----------------------- [ a 7 nargs()= 2 FALSE TRUE TRUE [ a 7 nargs()= 3 FALSE TRUE TRUE myfun a 7 nargs()= 2 FALSE TRUE TRUE myfun a 7 nargs()= 3 FALSE TRUE TRUE Function: [ (package base) x="foo", i="numeric", j="missing" function (x, i, j, ..., drop = TRUE) { cat(paste(match.call()), "\nnargs()=", nargs(), missing(i), missing(j), missing(drop), "\n\n") return(invisible(NULL)) } ######################################## > sessionInfo() R version 2.5.0 Under development (unstable) (2007-01-28 r40602) i686-pc-linux-gnu locale: LC_CTYPE=en_GB.UTF-8;LC_NUMERIC=C;LC_TIME=en_GB.UTF-8;LC_COLLATE=en_GB.UTF-8;LC_MONETARY=en_GB.UTF-8;LC_MESSAGES=en_GB.UTF-8;LC_PAPER=en_GB.UTF-8;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_GB.UTF-8;LC_IDENTIFICATION=C attached base packages: [1] "stats" "graphics" "grDevices" "utils" "datasets" "methods" [7] "base" Best wishes -- ------------------------------------------------------------------ Wolfgang Huber EBI/EMBL Cambridge UK http://www.ebi.ac.uk/huber
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