Hi Romain, hi Dirk,
sorry for posting here again, but I found something in some way connected to
this discussion - and pretty interesting concerning the Rcpp::as<>() function:
1. I create a class containing a list:
setClass("myclass", representation(par = "list"))
l <- list(lambda = array(0, dim = c(10,2)))
mclass <- new("myclass", par = l)
2. I compile a C++ function, that should reuse the memory of 'lambda' inside
the list:
library(inline)
cfunction <- cxxfunction(signature(myClass_R = "array"), body = 'Rcpp::S4
myclass(myClass_R); Rcpp::List parL((SEXP) myclass.slot("par")); arma::mat
armaPar(parL["lambda"].begin(), 10, 2, false, true); armaPar(0,0) = 1.2 ;return
Rcpp::wrap(myclass);', plugin = "RcppArmadillo")
I get an error:
Error in compileCode(f, code, language = language, verbose = verbose) :
Compilation ERROR, function(s)/method(s) not created! file6fc2ab39965.cpp: In
function ‘SEXPREC* file6fc2ab39965(SEXP)’:
file6fc2ab39965.cpp:30:109: error: ‘Rcpp::Vector<19>::NameProxy’ has no member
named ‘begin’
Rcpp::S4 myclass(myClass_R); Rcpp::List parL((SEXP) myclass.slot("par"));
arma::umat armaPar(parL["lambda"].begin(), 100, 10, false, true); armaPar(0,0)
= 1.2 ;return Rcpp::wrap(myclass);
^
make: *** [file6fc2ab39965.o] Error 1
In addition: Warning message:
running command '/Library/Frameworks/R.framework/Resources/bin/R CMD SHLIB
file6fc2ab39965.cpp 2> file6fc2ab39965.cpp.err.txt' had status 1
-----------------------------------------------------------
It seems, that the SEXP inside the List is not yet an Rcpp::NumericMatrix, so I
make it explicit to the arma::mat() constructor:
cfunction <- cxxfunction(signature(myClass_R = "array"), body = 'Rcpp::S4
myclass(myClass_R); Rcpp::List parL((SEXP) myclass.slot("par")); arma::mat
armaPar(Rcpp::as<Rcpp::NumericMatrix>(parL["lambda"]).begin(), 100, 10, false,
true); armaPar(0,0) = 1.2 ;return Rcpp::wrap(myclass);', plugin =
"RcppArmadillo")
That compiles.
If we let it run it gives us:
cfunction(mclass)
An object of class "myclass"
Slot "par":
$lambda
[,1] [,2]
[1,] 1.2 0
[2,] 0.0 0
[3,] 0.0 0
[4,] 0.0 0
[5,] 0.0 0
[6,] 0.0 0
[7,] 0.0 0
[8,] 0.0 0
[9,] 0.0 0
[10,] 0.0 0
So, we can see, that implicitly calling Rcpp::as<>() inside the constructor
arma::mat() avoids a copy by Rcpp::as<>() - which is just beautiful!
Best
Simon
On Jun 7, 2013, at 1:19 PM, Simon Zehnder <[email protected]> wrote:
> Thank you Romain!
>
> All clear now!
>
>
> Best
>
> Simon
>
> On Jun 7, 2013, at 1:13 PM, Romain Francois <[email protected]> wrote:
>
>> Le 07/06/13 13:09, Simon Zehnder a écrit :
>>> HI Dirk, hi Romain,
>>>
>>> allright, this is now clear to me, if I want to reuse memory, the allocated
>>> memory from R (so implicitly in C) must of course have the same type -
>>> otherwise the memory has a different size.
>>
>> so far, this is obvious.
>>
>>> On the other side I then assume, that the Rcpp:as<class M>() function makes
>>> a cast and therefore creates a copy with new allocated memory of the type
>>> included in M? Therefore a reuse of memory with this function is not
>>> possible.
>>
>> Depends what is M, but most of the time yes, as<> copies data.
>>
>>> Best
>>>
>>> Simon
>>>
>>>
>>> On Jun 6, 2013, at 8:31 PM, Dirk Eddelbuettel <[email protected]> wrote:
>>>
>>>>
>>>> On 6 June 2013 at 13:17, Dirk Eddelbuettel wrote:
>>>> |
>>>> | On 6 June 2013 at 19:05, Simon Zehnder wrote:
>>>> | | sorry I had overseen this message from you. Okay, so the explicit cast
>>>> to SEXP together with the assignment operator makes the deal. But it still
>>>> includes the reuse of memory right, i.e. the '=' does not call the copy
>>>> constructor?
>>>> |
>>>> | But how could an _unsigned int_ from Armadillo possibly have the same
>>>> value
>>>> | as a _signed int_ in R?
>>>> |
>>>> | Either you are efficient (no copy), or you are correct (with a copy). I
>>>> do
>>>> | not see how you could have both.
>>>>
>>>> Sorry -- please ignore this message.
>>>>
>>>> I had mistakenly assumed that you were still thinking about arma::umat to
>>>> integer. For direct int-to-int this is indeed efficient just like the
>>>> double-to-double is for arma::mat to NumericMatrix (and dito for vectors).
>>>> I
>>>> though that was a given -- maybe need to make this (even) more explicit in
>>>> the documentation.
>>>>
>>>> So in sum: you get correct and efficient behaviour if and only if you stick
>>>> with the types natively supported in Armadillo and R.
>>>>
>>>> Dirk
>>>>
>>>> --
>>>> Dirk Eddelbuettel | [email protected] | http://dirk.eddelbuettel.com
>>>
>>>
>>
>>
>> --
>> Romain Francois
>> Professional R Enthusiast
>> +33(0) 6 28 91 30 30
>>
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>>
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>
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