On 14 May 2011 at 23:12, Nick Sabbe wrote:
| I?ve been trying the following, with the main part ripped from rcpp-quickref:
|
| SEXP dfr2Mat(SEXP dfr)
A much easier way is to, say, call as.matrix() in R and then assign to an
NumericMatrix object in C++.
Another way is turn the Data.Frame into a list via as.list() as just pick off
column after column.
| {
| DataFrame df = dfr;
| int* dm = INTEGER( ::Rf_getAttrib( df, R_DimSymbol ) ) ;
| int rows = dm[0];
| int cols = dm[1];
| NumericMatrix retMat (rows, cols);
| for(int i = 0; i < cols; i++)
| {
| NumericVector curcol = df(i);
| NumericMatrix::Column cl = retMat.( _, i);
Why is retMat on the right-hand side if you try to fill it? Makes no real
sense.
| cl = curcol;
| }
| return retMat;
| }
I can see no straightforward way to write given how objects are organized
internally. Once a Rcpp::DataFrame object is instantiated, you can call
size() which gives you the number of columns. So here is a really
complicated way to do this, but let me reiterate that I think you are
starting from the wrong starting point: if your data.frame really is a
matrix, just use a matrix:
R> require(inline)
Loading required package: inline
R>
R> df2mat <- cxxfunction(signature(Dsexp="ANY"), plugin="Rcpp", body='
+ // construct the data.frame object
+ Rcpp::DataFrame DF = Rcpp::DataFrame(Dsexp);
+
+ // we get ncol() from DF
+ int k = DF.size();
+
+ // but for nrow() we need to assign first; one way is:
+ Rcpp::NumericVector V = DF[0];
+ int n = V.size();
+
+ Rcpp::NumericMatrix M(n,k);
+
+ for (int i=0; i<k; i++) {
+ V = DF[i];
+ M(_,i) = V; // one way to assign using sugar operator _
+ }
+
+ return M;
+ ')
R> M <- df2mat(data.frame(a=1:5, b=seq(1.1,5.5,by=1.1)))
R> M
[,1] [,2]
[1,] 1 1.1
[2,] 2 2.2
[3,] 3 3.3
[4,] 4 4.4
[5,] 5 5.5
R> class(M)
[1] "matrix"
R>
Hope this helps, Dirk
--
Gauss once played himself in a zero-sum game and won $50.
-- #11 at http://www.gaussfacts.com
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