On 10 May 2013 at 13:34, Matwey V. Kornilov wrote:
| Thanks, It is what I was looking for. But now, I poorly understand
| environment conception. My initial C function in invoked from R (in some
| environment I suppose), how do I know this env, to provide it to eval()?
| Or, may I just make a clean env?
Given that you seem a little fuzzy about all this, may I suggest a pivot over
to Rcpp? While it uses C++ features, you are not really forced to use C++.
Here is one really quick example:
R> library(Rcpp)
R> cppFunction('NumericVector callRonVec(NumericVector x, Function f) {
NumericVector res = f(x); return(res); }')
R> callRonVec( (1:100)^2, fivenum)
[1] 1.0 650.5 2550.5 5700.5 10000.0
R> fivenum( (1:100)^2 ) # obviously the same
[1] 1.0 650.5 2550.5 5700.5 10000.0
R>
All we are doing here is instantiating some variable. You can access their
content and modify it C style if you so desire, or you can use the C++
features you like and ignore any others. As you mentioned environment, you
can also pass down any R environment.
You can also combine this with other packages such as RcppArmadillo which
give you easy-to-use idioms often modeled after Matlab. One such example is
the solve() function at the C++ level. Another quick example:
R> X <- as.matrix(cbind(1:100, sqrt(1:100))); y <- rowSums(X) + rnorm(100)
R> lm.fit(X,y)$coefficients # fit in R as a baseline
x1 x2
1.003357 0.981233
R> cppFunction('arma::vec mySolve(arma::mat x, arma::vec y) {
return(solve(x,y)); }', depends="RcppArmadillo")
R> mySolve(X, y) # no surprise, we get the same answer
[,1]
[1,] 1.003357
[2,] 0.981233
R>
This use the Armadillo matrix and vector types, and calls solve() for you --
which will dispatch to the same BLAS functions R uses, but gets there at no
extra effort for you (besides having to read up on (Rcpp)Armadillo). As a
side benefit, these things tend to be faster in C++.
Hope this helps. The introductory vignettes to Rcpp and RcppArmadillo are
also available as papers in JSS (in 2011) and CSDA (2013, in press), and
there is a fair bit of other documentation out there.
Dirk
| 10.05.2013 00:13, Gabriel Becker пишет:
| > Matwey,
| >
| > There are a number of ways to do this, but it depends on what exactly you
| > want. Do you want to execute a call to an actual R function from within C,
| > or do you want to directly call one of R's internal C functions (which may
| > work but is not future-safe unless it is part of the official API).
| >
| > If its the first, see Martin Morgan's post here:
| > http://stackoverflow.com/questions/7457635/calling-r-function-from-c for
| > more detail about the approach I believe Simon is referring to. As for the
| > second, they are normal C functions, but I believe the consensus is that if
| > they aren't part of the API you are on your own figuring out how they work
| > (the source code is available for this of course).
| >
| > Hope that helps,
| > ~G
|
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--
Dirk Eddelbuettel | e...@debian.org | http://dirk.eddelbuettel.com
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