[R] Pass vector as multiple parameters (as in python f(*x))
Jeff Newmiller
jdnewmil at dcn.davis.CA.us
Sat Jan 26 07:49:42 CET 2013
How about (assuming the variables you defined):
ms <- matrix(unlist(vs), ncol=2,byrow=TRUE)
m[ms]
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Sent from my phone. Please excuse my brevity.
Carlos Pita <carlosjosepita at 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:<jdnewmil at 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 <carlosjosepita at 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 at 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.
>>
>
>______________________________________________
>R-help at 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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