On 13/11/2015 12:53 PM, ALBERTO VIEIRA FERREIRA MONTEIRO wrote:
I have another environment question.
I understand why this works as expected:
f.factory <- function()
{
y <- 2
fname <- paste("plus", y, sep = ".")
f <- function(x) x + y
assign(fname, f, envir = globalenv())
}
f.factory()
plus.2(2) # 4
and I also understand why this does NOT work:
f.factory <- function()
{
for (y in 2:3) {
fname <- paste("plus", y, sep = ".")
f <- function(x) x + y
assign(fname, f, envir = globalenv())
}
}
f.factory()
plus.2(2) # 5
(the reason is that both plus.2 and plus.3 have the
same environment as f.factory when f.factory terminates,
which assign 2 to variable y in the first case and 3 in
the second case)
However, I don't know an elegant way to adapt f.factory
so that it works as expected. Any suggestions?
I think Bill answered your question. I'd suggest that you should ask a
different question. It's generally a bad idea to use assign(),
especially for assignments into the global environment. Your f.factory
should return a value, it shouldn't modify globalenv(). It's often a
bad idea to refer to the environment explicitly at all. So my
recommended solution might be this variation on Bill's:
f.factory4 <- function()
{
result <- list()
for (y in 2:3) {
result[[y]] <- local({
ylocal <- y
function(x) x + ylocal
})
names(result)[y] <- paste("plus", y, sep = ".")
}
result
}
The "names" line is optional; with it, you can use
f <- f.factory4()
f$plus.2(2)
but with or without it you can use
f[[2]](2)
Duncan Murdoch
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