[Rd] Pb with lapply()
hpages at fhcrc.org
hpages at fhcrc.org
Thu Jan 31 19:26:31 CET 2008
Hi,
If needed, lapply() tries to convert its first argument into a list
before it starts doing something with it:
> lapply
function (X, FUN, ...)
{
FUN <- match.fun(FUN)
if (!is.vector(X) || is.object(X))
X <- as.list(X)
.Internal(lapply(X, FUN))
}
But in practice, things don't always seem to "work" as suggested by
this code (at least to the eyes of a naive user).
I have defined an "as.list" method for my S4 class "A":
> setClass("A", representation(data="list"))
[1] "A"
> setMethod("as.list", "A", function(x, ...) x at data)
Creating a new generic function for "as.list" in ".GlobalEnv"
[1] "as.list"
Testing it:
> a <- new("A", data=list(8, 2:0))
> as.list(a)
[[1]]
[1] 8
[[2]]
[1] 2 1 0
OK.
But lapply() doesn't work on 'a':
> lapply(a, typeof)
Error in as.vector(x, "list") : cannot type 'S4' coerce to vector
I still have to do the 'as.list(a)' part myself for things to work:
> lapply(as.list(a), typeof)
[[1]]
[1] "double"
[[2]]
[1] "integer"
Seems like using force() inside lapply() would solve the problem:
lapply2 <- function(X, FUN, ...)
{
FUN <- match.fun(FUN)
if (!is.vector(X) || is.object(X))
X <- force(as.list(X))
.Internal(lapply(X, FUN))
}
It works now:
> lapply2(a, typeof)
[[1]]
[1] "double"
[[2]]
[1] "integer"
Cheers,
H.
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