This an alternating way of doing it using a list if you know the
argument names in
the function definition i.e. ?formals and ?alist, But would change
the default values of the function. Probably not you wanted.
> f <- function(x,y,z) x+y+z
> args<-alist(x=5,y=6,z=7)
> formals(f) <- args
> f()
[1] 18
On 26 January 2013 01:46, Carlos Pita <carlosjosep...@gmail.com> wrote:
> Thanks Bert, do.call is exactly what I was looking for. What in lisp
> is apply and in python f(*v).
>
>> Your whole premise that the arguments of a function should be mappable to
>> elements of a vector seems contrary to good R programming practice.
>
> Jeff I didn't pretend to imply that the mapping should by always
> possible. lists for positional arguments and named lists for named
> arguments would do the trick most of the times. It's pretty common in
> dynamic languages.
>
> That said, the specific task I have in mind is to index an array of an
> arbitrary dimension n by a list of length n vectors, each one
> representing <x1,...,xn> coordinates.
>
> For example, if n=2, the array is the matrix m, and the list of vectors is vs:
>
> m=matrix(1:16,4)
> vs = list(c(2,3),c(2,2),c(1,1))
>
> Then do.call would allow me to index m as follows:
>
> lapply(vs, function(v) { do.call(`[`, append(list(m), v)) })
>
> Alternatively:
>
> f = function (...) { m[...] }
> lapply(vs, function(v) { do.call(f, as.list(v)) })
>
> Of course, I could just do m[v[1],v[2]] in this case, but the point is
> that the dimension n would be a parameter of my function, not a
> constant.
>
> But if you know of a better or more r-esque solution I would be very
> glad to hear of it.
>
> Best regards
> --
> Carlos
>
>
> Best regards
> --
> Carlos
>
> Consider changing the called function's handling of arguments instead
> to accept the vector of data directly if a vector makes sense, or to a
> list if the arguments have a variety of types.
>> ---------------------------------------------------------------------------
>> Jeff Newmiller The ..... ..... Go Live...
>> DCN:<jdnew...@dcn.davis.ca.us> Basics: ##.#. ##.#. Live Go...
>> Live: OO#.. Dead: OO#.. Playing
>> Research Engineer (Solar/Batteries O.O#. #.O#. with
>> /Software/Embedded Controllers) .OO#. .OO#. rocks...1k
>> ---------------------------------------------------------------------------
>> Sent from my phone. Please excuse my brevity.
>>
>> Carlos Pita <carlosjosep...@gmail.com> wrote:
>>
>>>Hi,
>>>
>>>I want to know if it's possible to pass a vector v=c(x,y,...) to a
>>>function f(x,y,...) so that each vector element corresponds to a
>>>formal argument of the function. For python programmers: f(*v).
>>>
>>>Specifically, what I'm trying to achieve is: given a list of
>>>coordinates l=list(c(x1,y1,z1), c(x2,y2,z2),...) I would like to
>>>obtain the corresponding elements in some array A (3-dim in this
>>>case). That is: A[x1,y1,z1], A[x2,y2,z2],....
>>>
>>>One way would be to transform l=list(c(x1,y1,z1), c(x2,y2,z2),...) to
>>>l2=list(c(x1,x2,...),c(y1,y2,...),c(z1,z2,...)) and then (if this is
>>>possible at all) execute the equivalent to A[*l2].
>>>
>>>Another way would be to lapply function(xyz) { A[*xyz] } to each
>>>coordinate vector in l. In any case I need the f(*v) equivalent.
>>>
>>>Please take into account that, despite the 3-dim example, I need to
>>>implement the above to accept n-dim vectors for arbitrary n, so
>>>something like x<-xyz[1], y<-xyz[2], z<-xyz[3] wouldn't fit the bill.
>>>
>>>Any other suggested solution would be appreciated.
>>>
>>>Best regards
>>>--
>>>Carlos
>>>
>>>______________________________________________
>>>R-help@r-project.org mailing list
>>>https://stat.ethz.ch/mailman/listinfo/r-help
>>>PLEASE do read the posting guide
>>>http://www.R-project.org/posting-guide.html
>>>and provide commented, minimal, self-contained, reproducible code.
>>
>
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
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