On 4/27/05, Ali - <[EMAIL PROTECTED]> wrote:
>
>
>
> > >
> > > Assume we have a function like:
> > >
> > > foo <- function(x, y)
> > >
> > > how is it possible to define a binary indexing operator, denoted by $,
> >so
> > > that
> > >
> > > x$y
> > >
> > > functions the same as
> > >
> > > foo(x, y)
> >
> > Here is an example. Note that $ does not evaluate y so you have
> >to do it yourself:
> >
> >x <- structure(3, class = "myclass")
> >y <- 5
> >foo <- function(x,y) x+y
> >"$.myclass" <- function(x, i) { i <- eval.parent(parse(text=i)); foo(x,
> i)
> >}
> >x$y # structure(8, class = "myclass")
>
> what about this approach:
>
> foo <- function(x, y) x+y
> assign("$", foo)
>
> would this overwrite $
Yes.
and make R to forget its definitions in the global
environment?
Yes.
Your construct might still be used in a local environment.
f <- function(x,y) {
"$" <- function(x,y) x+y
x$y
}
f(1,2) # 3
# or
z <- local({
"$" <- function(x,y) x+y
x <- y <- 3
x$y
})
z # 6
works and outside of f and the local, $ works normally.
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