On Wed, Jul 29, 2015 at 10:37 AM, Dirk Eddelbuettel <e...@debian.org> wrote:
> You misunderstand. We communicate by SEXP. Where the P stands for pointer.
> IE even with
>
> R> M <- as.data.frame(matrix(rnorm(1e6, 1e3)))
> R> object.size(M)
> 8000672 bytes
> R>
>
> we'd still only pass the same 56 bytes a SEXP takes. See eg
> https://cran.r-project.org/doc/manuals/R-ints.html#SEXPs and play with memory
> profiling in R.
I tried memory profiling both of your versions with a long vector, and
found that the recommended Rcpp approach made an additional 8GB copy.
Is there a way to avoid this extra copy without resorting to in place
modification?
--nate
nate@ubuntu:~/R/byreference$ less abs.R
library(Rcpp)
cppFunction("NumericVector absCopy(NumericVector & x) { return abs(x); }")
cppFunction("void absInPlace(NumericVector & x) { x = abs(x); }")
xOrig = rnorm(1000*1000*1000)
xRef = xOrig # shallow copy shares memory
xCopy = xOrig * 1 # deep copy is independent
Rprofmem("absInPlace.txt")
absInPlace(xOrig)
Rprofmem(NULL)
identical(xOrig, xRef)
identical(xOrig, xCopy)
Rprofmem("absCopy.txt")
xCopy = absCopy(xCopy)
Rprofmem(NULL)
identical(xOrig, xRef)
identical(xOrig, xCopy)
nate@ubuntu:~/R/byreference$ Rscript abs.R
[1] TRUE
[1] FALSE
[1] TRUE
[1] TRUE
nate@ubuntu:~/R/byreference$ cat absInPlace.txt
2544 :"<Anonymous>" "absInPlace"
nate@ubuntu:~/R/byreference$ cat absCopy.txt
8000000040 :"<Anonymous>" "absCopy"
2544 :"<Anonymous>" "absCopy"
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