Re: [Rd] How to overload the assignment operator?
are you looking for setReplaceMethod?
hth
Matthias
Jens Oehlschlägel wrote:
Dear all,
what is the proper way to make the assignment operator generic and define
methods depending on the class of the assigned value?
Best regards
Jens Oehlschlägel
P.S. I vaguely remember that this was possible in S+. In R I tried to no
avail:
# using this like h-1:3 gives Error: in `-.default`(h, 1:3) : invalid
(do_set) left-hand side to assignment
-.default - get(-)
# using this does fail on subassignments like: h - 1:3 ; h[1] - 7 (h
still is 1:3)
-.default - function(x, value){
assign(deparse(substitute(x)), value, parent.frame())
invisible(x)
}
# this seems to work
- - function(x, value){
UseMethod(-, value)
}
# whenever the assigned value has class 'ff' I want to do execute something
like
-.ff - function(x, value){
y - clone(value)
assign(deparse(substitute(x)), y, parent.frame())
y
}
version
_
platform i386-pc-mingw32
arch i386
os mingw32
system i386, mingw32
status
major 2
minor 6.0
year 2007
month 10
day03
svn rev43063
language R
version.string R version 2.6.0 (2007-10-03)
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Re: [Rd] How to overload the assignment operator?
I think the question is not about setReplaceMethod, here is the idea:
## setReplaceMethod-like situation:
names(x) - c(a,b)
## the question of interest
class(x)
[1] myClass
y - x ## this to run a user-defined clone method for class 'myClass'
Why is this important - if x contains data that actually needs to be
duplicated this would come handy. I'd like to know the solution as well.
Maybe it's my ignorance that I don't know the answer and the response
will be RTFM - fine, just point out where :)
Best,
Oleg
On Tue, 2007-11-13 at 14:52 +0100, Matthias Kohl wrote:
are you looking for setReplaceMethod?
hth
Matthias
Jens Oehlschlägel wrote:
Dear all,
what is the proper way to make the assignment operator generic and define
methods depending on the class of the assigned value?
Best regards
Jens Oehlschlägel
P.S. I vaguely remember that this was possible in S+. In R I tried to no
avail:
# using this like h-1:3 gives Error: in `-.default`(h, 1:3) : invalid
(do_set) left-hand side to assignment
-.default - get(-)
# using this does fail on subassignments like: h - 1:3 ; h[1] - 7 (h
still is 1:3)
-.default - function(x, value){
assign(deparse(substitute(x)), value, parent.frame())
invisible(x)
}
# this seems to work
- - function(x, value){
UseMethod(-, value)
}
# whenever the assigned value has class 'ff' I want to do execute
something like
-.ff - function(x, value){
y - clone(value)
assign(deparse(substitute(x)), y, parent.frame())
y
}
version
_
platform i386-pc-mingw32
arch i386
os mingw32
system i386, mingw32
status
major 2
minor 6.0
year 2007
month 10
day03
svn rev43063
language R
version.string R version 2.6.0 (2007-10-03)
--
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Dr Oleg Sklyar * EBI-EMBL, Cambridge CB10 1SD, UK * +44-1223-494466
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Re: [Rd] How to overload the assignment operator?
Thanks Matthias, are you looking for setReplaceMethod? So far the package I m writing has avoided using anything from S4 and the implications of touching S4 are not clear to me. The package aims on providing an alternative to 'atomic' data stored in ram, i.e. large atomic data stored on disk. I need some advice how to do this maximally performant, which probably means pure S3!? Best regards Jens Oehlschlägel -- __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
Re: [Rd] How to overload the assignment operator?
On Nov 13, 2007, at 9:19 AM, Jens Oehlschlägel wrote: Thanks Matthias, are you looking for setReplaceMethod? So far the package I m writing has avoided using anything from S4 and the implications of touching S4 are not clear to me. The package aims on providing an alternative to 'atomic' data stored in ram, i.e. large atomic data stored on disk. I need some advice how to do this maximally performant, which probably means pure S3!? You cannot use S3 here, because you want to dispatch on the *second* argument. I don't think you want to do what you described - you would slow down everything in R considerably just by making `-` a generic (and in fact you cannot do that for a good reason). Why don't you take the external pointer approach that many others take to provide proxy objects to external data? (DB access, mem-mapped files, cross-language objects, etc.) That allows you to define your storage semantics very efficiently in C. You can still choose to define any syntactic sugar you want in either S3 or S4. Cheers, Simon __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
Re: [Rd] How to overload the assignment operator?
On Tue, 13 Nov 2007, Jens Oehlschlägel wrote: Thanks Matthias, are you looking for setReplaceMethod? So far the package I m writing has avoided using anything from S4 and the implications of touching S4 are not clear to me. The package aims on providing an alternative to 'atomic' data stored in ram, i.e. large atomic data stored on disk. I need some advice how to do this maximally performant, which probably means pure S3!? setReplaceMethod() is just syntactic sugar for setting an S4 method on a replacement function (read the function definition to see so). You can set S3 replacement methods, and the S4 mechanism just piggy-backs on that. I think the conceptual problem is that the assignment operator does not actually do any copying: it creates a binding of a symbol to a value. Any copying which occurs happens when the value is (potentially) changed. There is no provision for that to depend on the class (rather than the type) of the object. Since external pointers are never duplicated, you ought to be able to take advantage of that to design the copying semantics you want. -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UKFax: +44 1865 272595__ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
Re: [Rd] How to overload the assignment operator?
Check out the g.data package in case that's what you are looking for. It uses promises until the data is actually used. On Nov 13, 2007 9:19 AM, Jens Oehlschlägel [EMAIL PROTECTED] wrote: Thanks Matthias, are you looking for setReplaceMethod? So far the package I m writing has avoided using anything from S4 and the implications of touching S4 are not clear to me. The package aims on providing an alternative to 'atomic' data stored in ram, i.e. large atomic data stored on disk. I need some advice how to do this maximally performant, which probably means pure S3!? Best regards Jens Oehlschlägel -- __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
Re: [Rd] How to overload the assignment operator?
Thank you Brian, setReplaceMethod() is just syntactic sugar for setting an S4 method on a replacement function (read the function definition to see so). You can set S3 replacement methods, and the S4 mechanism just piggy-backs on that. So I understand that setReplaceMethod will not help. I think the conceptual problem is that the assignment operator does not actually do any copying: it creates a binding of a symbol to a value. Any copying which occurs happens when the value is (potentially) changed. I would be even happier if the cloning would only occur on any attempt to change the external pointer / proxy-object. There is no provision for that to depend on the class (rather than the type) of the object. Mh, unless the internal copying mechanism would call a clone generic for non-atomic objects Since external pointers are never duplicated, you ought to be able to take advantage of that to design the copying semantics you want. How that? How do I know that any user has assigned/modified the external pointer (or a proxy object containing the external pointer) such that I can invoke the cloning? Best regards Jens Oehlschlägel -- __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
Re: [Rd] How to overload the assignment operator?
Thanks Simon,
You cannot use S3 here, because you want to dispatch on the *second*
argument.
- - function(x, value)UseMethod(-, value)
DOES dispatch on the second argument (see the dispatchsecond example below)
Why don't you take the external pointer approach that many others take
to provide proxy objects to external data? (DB access, mem-mapped
files, cross-language objects, etc.) That allows you to define your
storage semantics very efficiently in C. You can still choose to
define any syntactic sugar you want in either S3 or S4.
I AM using the external pointer approach and this works verly well - if one
tolerates that the external data is not duplicated when the proxy object is
copied. I was wondering however, if it is possible to perfectly mimic R's
copying semantics: duplicate external object (and the external pointer) on
assignment (or even better only on modify after assignment).
Best regards
Jens Oehlschlägel
dispatchsecond - function(first, second)
+ UseMethod(dispatchsecond, second)
dispatchsecond.default - function(first, second){
+ cat(here default\n)
+ }
dispatchsecond.ff - function(first, second){
+ cat(here ff\n)
+ }
default - 1
ff - 1
class(ff) - ff
dispatchsecond(1,default)
here default
dispatchsecond(1,ff)
here ff
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Re: [Rd] How to overload the assignment operator?
Thanks Simon,
You cannot use S3 here, because you want to dispatch on the *second*
argument.
- - function(x, value)UseMethod(-, value)
DOES dispatch on the second argument (see the dispatchsecond example below)
Why don't you take the external pointer approach that many others take
to provide proxy objects to external data? (DB access, mem-mapped
files, cross-language objects, etc.) That allows you to define your
storage semantics very efficiently in C. You can still choose to
define any syntactic sugar you want in either S3 or S4.
I AM using the external pointer approach and this works verly well - if one
tolerates that the external data is not duplicated when the proxy object is
copied. I was wondering however, if it is possible to perfectly mimic R's
copying semantics: duplicate external object (and the external pointer) on
assignment (or even better only on modify after assignment).
Best regards
Jens Oehlschlägel
dispatchsecond - function(first, second)
+ UseMethod(dispatchsecond, second)
dispatchsecond.default - function(first, second){
+ cat(here default\n)
+ }
dispatchsecond.ff - function(first, second){
+ cat(here ff\n)
+ }
default - 1
ff - 1
class(ff) - ff
dispatchsecond(1,default)
here default
dispatchsecond(1,ff)
here ff
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Re: [Rd] How to overload the assignment operator?
On Tue, 13 Nov 2007, Jens Oehlschlägel wrote: Thank you Brian, setReplaceMethod() is just syntactic sugar for setting an S4 method on a replacement function (read the function definition to see so). You can set S3 replacement methods, and the S4 mechanism just piggy-backs on that. So I understand that setReplaceMethod will not help. I think the conceptual problem is that the assignment operator does not actually do any copying: it creates a binding of a symbol to a value. Any copying which occurs happens when the value is (potentially) changed. I would be even happier if the cloning would only occur on any attempt to change the external pointer / proxy-object. There is no provision for that to depend on the class (rather than the type) of the object. Mh, unless the internal copying mechanism would call a clone generic for non-atomic objects But as I said, there is no provision for that. Nor is there going to be. One reason is performance, as Simon has hinted. Another is consistency: duplication might well be called from places where class is being ignored. Since external pointers are never duplicated, you ought to be able to take advantage of that to design the copying semantics you want. How that? How do I know that any user has assigned/modified the external pointer (or a proxy object containing the external pointer) such that I can invoke the cloning? I don't even know what you want to do. But I don't think copying is the place to find out if a user changed an object: presumably it was done via your interface. -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UKFax: +44 1865 272595__ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
