[Rcpp-devel] Dynamic Wrapping and Recursion with Rcpp - using an R function?

[Tal Galili]

Hi Kevin,

As to the "fu" function, I didn't return "node" since I thought the change
was on the mutable object. But from your (very detailed, thank you!)
answer, I am learning that my hope for a general way of doing what I wanted
is not feasible.

Again, thank you for the response - it was very informative!

Best,
Tal





----------------Contact
Details:-------------------------------------------------------
Contact me: Tal.Galili at gmail.com |
Read me: www.talgalili.com (Hebrew) | www.biostatistics.co.il (Hebrew) |
www.r-statistics.com (English)
----------------------------------------------------------------------------------------------



On Sat, Jul 27, 2013 at 12:51 AM, Kevin Ushey <kevinushey at gmail.com> wrote:

> Hi Tal,
>
> A couple points:
>
> 1) Your R function `fu` doesn't specify a return. In addition, calling an
> R function in C++ code is still going to fall into the same pitfalls of
> calling it directly in R -- you're going to make a copy, and going to have
> to reassign the copy. You can cheat by using `<<-` but this is not
> recommended.
>
> Case-in-point:
>
> cppFunction('void test(NumericVector x, Function FUN) { FUN(x); }')
> x <- c(1, 2, 3)
> f <- function(x) { x <- x + 100 }
> g <- function(x) { return(x + 100) }
> h <- function(x) { x <<- x + 100 }
> test(x, f)
> x ## no change
> test(x, g)
> x ## no change
> test(x, h)
> x ## changed
>
> If you care about speed, passing R functions to your Rcpp code is not
> recommended.
>
> 2) You don't switch over the RTYPE in your for loop. The elements in your
> list are either going to be lists (VECSXPs) if they're another branch of
> the tree, or non-lists otherwise (probably numeric / REALSXP?). I imagine
> the behavior you want depends on the type of object you encounter while
> recursing.
>
> If you really want to do things in place and do it quickly, do it entirely
> in C++. Calling R functions from C++ isn't going to help.
>
> Finally, if you want to set attributes explicitly, check out the `.attr`
> function.
>
> -Kevin
>
>
> On Fri, Jul 26, 2013 at 2:06 PM, Krzysztof Sakrejda <
> krzysztof.sakrejda at gmail.com> wrote:
>
>> Make the wrapper a reference class which has a field for the data.
>> When the wrapper is initialized, pass the data as an argument and it
>> will be copied when the initialize method runs. Works in my project...
>> or am I missing something here?
>>
>> Krzysztof
>>
>> On Fri, Jul 26, 2013 at 4:58 PM, Tal Galili <tal.galili at gmail.com> wrote:
>> > Hi Hadley,
>> >
>> > Regarding the cloning of the object in C++: since I will want to use the
>> > function recursively, I will either have the cloning in the wrapper R
>> > function. And if I discover that is not possible (I haven't tried it
>> yet),
>> > my next thought was to split the work into two functions, in one there
>> will
>> > be the cloning, and the other will do the recursion.
>> > Since the example I gave in the first e-mail doesn't work (help is
>> > welcomed), I am not there yet :)
>> >
>> > As for as.dendrogram, that is the case with hclust object. However,
>> these
>> > objects has limitations when it comes to trees which are NOT binary
>> trees.
>> > So one of the things I started doing with dendextend is to create
>> various
>> > functions that will work for non-binary trees (which I previously had to
>> > work with).
>> >
>> > Tal
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> > ----------------Contact
>> > Details:-------------------------------------------------------
>> > Contact me: Tal.Galili at gmail.com |
>> > Read me: www.talgalili.com (Hebrew) | www.biostatistics.co.il (Hebrew)
>> |
>> > www.r-statistics.com (English)
>> >
>> ----------------------------------------------------------------------------------------------
>> >
>> >
>> >
>> > On Fri, Jul 26, 2013 at 7:07 PM, Hadley Wickham <h.wickham at gmail.com>
>> wrote:
>> >>
>> >> > I understand your point, and am not sure how to proceed without it.
>> >>
>> >> Just make sure you clone the initial list once, or use another C++
>> >> data structure (e.g. std::vector) that can grow efficiently.
>> >>
>> >> Alternatively, you could create your own alternative to as.dendrogram
>> >> that doesn't create a hierarchical structure.  (That's what I'd try
>> >> first)
>> >>
>> >> Hadley
>> >>
>> >> --
>> >> Chief Scientist, RStudio
>> >> http://had.co.nz/
>> >
>> >
>> >
>> > _______________________________________________
>> > Rcpp-devel mailing list
>> > Rcpp-devel at lists.r-forge.r-project.org
>> > https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
>>
>>
>>
>> --
>>
>> Krzysztof Sakrejda
>>
>> Organismic and Evolutionary Biology
>> University of Massachusetts, Amherst
>> 319 Morrill Science Center South
>> 611 N. Pleasant Street
>> Amherst, MA 01003
>>
>> work #: 413-325-6555
>> email: sakrejda at cns.umass.edu
>> -----------------------------------------------
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>>
>
>
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