Rolf Turner wrote:
I have been trying to write a function mv(a,b) to move an
object a to object b. It returns no value, but only
exists for this side effect. Basically it just does
b <- a; rm(a). With some checking and prompting about
over-writing.
The thing is, I'd like to be able to use either call by
name or call by value syntax. I.e. I want to set up my
argument processing so that
mv(a,b)
mv("a",b)
mv(a,"b")
mv("a","b")
are all equivalent. I thought I had achieved this using
anm <- if(is.character(substitute(a))) a else deparse(substitute(a))
bnm <- if(is.character(substitute(b))) b else deparse(substitute(b))
and then working with ``anm'' and ``bnm''.
However the real reason I wanted to be able to use text strings
rather than names as arguments was so that I could do things like
mv(paste("x",i,sep="."),paste("y",i,sep="."))
(and use such a structure in a for loop, and so forth).
With the paste construction I seem to have to do something like putting
in an ``eval'', as in eval(substitute(a)). But then the whole thing
falls over when a is a name, i.e. mv(a,b) doesn't work any more.
Is there an incantation that will allow me to accomplish all of my
desiderata?
Rolf,
are you just trying to turn the input into character?
If so, the following may help, but I'd be surprised if
there aren't plenty of situations where it won't work.
I ain't no guru.
g <- function(x){
x <- substitute(x)
if(is.name(x)) {
xnm <- deparse(x)
}
else {
if(is.language(x)) {
xnm <- eval(x)
}
else xnm <- x
}
get(xnm)
}
u <- 1:5
v <- letters[1:5]
u.v <- 5:1
g(u)
g('u')
g(v)
g('v')
g(paste('u', 'v', sep='.'))
-Peter Ehlers
Thanks.
cheers,
Rolf Turner
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--
Peter Ehlers
University of Calgary
403.202.3921
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