Re: [R] Defining binary indexing operators
On 4/27/05, Ali - <[EMAIL PROTECTED]> wrote:
>
>
> > > >
> > > > 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")
> > >
>
> If I got it right, in the above example you provided '$' is defined as a
> method for a S3 class. How is it possible to do the same with a S4 class.
> If
> this is not possible, what is the best way to define the '$' operator
> whose
> first arguments is a S4 object and doesn't overwrite the global
> definition?
>
> The myclass example is defined as an S3 method. In the above its defined
> as a function, not a method.
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Re: [R] Defining binary indexing operators
> >
> > 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")
>
If I got it right, in the above example you provided '$' is defined as a
method for a S3 class. How is it possible to do the same with a S4 class. If
this is not possible, what is the best way to define the '$' operator whose
first arguments is a S4 object and doesn't overwrite the global definition?
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Re: [R] Defining binary indexing operators
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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Re: [R] Defining binary indexing operators
Excuse me! I misunderstood the question, and indeed, it is necessary be
that complicated when you try to make x$y behave the same as foo(x,y),
rather than foo(x,"y") (doing the former would be inadvisible, as I
think someelse pointed out too.)
Tony Plate wrote:
It's not necessary to be that complicated, is it? AFAIK, the '$'
operator is treated specially by the parser so that its RHS is treated
as a string, not a variable name. Hence, a method for "$" can just take
the indexing argument directly as given -- no need for any fancy
language tricks (eval(), etc.)
> x <- structure(3, class = "myclass")
> y <- 5
> foo <- function(x,y) paste(x, " indexed by '", y, "'", sep="")
> foo(x, y)
[1] "3 indexed by '5'"
> "$.myclass" <- foo
> x$y
[1] "3 indexed by 'y'"
>
The point of the above example is that foo(x,y) behaves differently from
x$y even when both call the same function: foo(x,y) uses the value of
the variable 'y', whereas x$y uses the string "y". This is as desired
for an indexing operator "$".
-- Tony Plate
Gabor Grothendieck wrote:
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")
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Re: [R] Defining binary indexing operators
>
> 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 $ and make R to forget its definitions in the global
environment?
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Re: [R] Defining binary indexing operators
It's not necessary to be that complicated, is it? AFAIK, the '$'
operator is treated specially by the parser so that its RHS is treated
as a string, not a variable name. Hence, a method for "$" can just take
the indexing argument directly as given -- no need for any fancy
language tricks (eval(), etc.)
> x <- structure(3, class = "myclass")
> y <- 5
> foo <- function(x,y) paste(x, " indexed by '", y, "'", sep="")
> foo(x, y)
[1] "3 indexed by '5'"
> "$.myclass" <- foo
> x$y
[1] "3 indexed by 'y'"
>
The point of the above example is that foo(x,y) behaves differently from
x$y even when both call the same function: foo(x,y) uses the value of
the variable 'y', whereas x$y uses the string "y". This is as desired
for an indexing operator "$".
-- Tony Plate
Gabor Grothendieck wrote:
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")
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Re: [R] Defining binary indexing operators
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")
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RE: [R] Defining binary indexing operators
I should have added that if you're not wedded to "$" you can do
$ "%f%" <- function(x,y) foo(x,y)
for whatever name "f" you want, and then %f% is a binary infix operator form
of foo().
Reid Huntsinger
-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Huntsinger, Reid
Sent: Wednesday, April 27, 2005 4:10 PM
To: 'Ali -'; r-help@stat.math.ethz.ch
Subject: RE: [R] Defining binary indexing operators
That sounds like a recipe for headaches. If you want to use "x$y" because
you want a certain kind of "x" to act like a list with components for
certain "y", then you probably want to make a class of objects (x) which
have "x$y" implemented as foo(x,y). That way you won't break existing code.
Reid Huntsinger
-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Ali -
Sent: Wednesday, April 27, 2005 3:11 PM
To: r-help@stat.math.ethz.ch
Subject: [R] Defining binary indexing operators
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)
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RE: [R] Defining binary indexing operators
That sounds like a recipe for headaches. If you want to use "x$y" because you want a certain kind of "x" to act like a list with components for certain "y", then you probably want to make a class of objects (x) which have "x$y" implemented as foo(x,y). That way you won't break existing code. Reid Huntsinger -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Ali - Sent: Wednesday, April 27, 2005 3:11 PM To: r-help@stat.math.ethz.ch Subject: [R] Defining binary indexing operators 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) __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
[R] Defining binary indexing operators
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) __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
