Constructing 3D array in Rcpp
r, rcpp
Solution
It is doable, but a little painful. I guess a decent (and tested) contribution for new constructor or helper function would be appreciated.
In the meantime, you can do what the example below does. But be careful about row-major and col-major etc. Another option is RcppArmadillo which has a proper 'Cube' type generalizing matrices to 3-d.
R> library(inline)
R> fx <- cxxfunction(signature(vs="numeric", ds="integer"), plugin="Rcpp", body='
+ Rcpp::NumericVector v(vs); // get the data
+ Rcpp::Dimension d(ds); // get the dim object
+ Rcpp::NumericVector r(d); // create vec. with correct dims
+ std::copy(v.begin(), v.end(), r.begin()); // and copy
+ return Rcpp::List::create(v, d, r);
+ ')
R> fx(1:8, c(2,2,2))
[[1]]
[1] 1 2 3 4 5 6 7 8
[[2]]
[1] 2 2 2
[[3]]
, , 1
[,1] [,2]
[1,] 1 3
[2,] 2 4
, , 2
[,1] [,2]
[1,] 5 7
[2,] 6 8
R>
Problem
I am trying to map a 1D array onto 3D array using provided list of dimensions. Here are my components: ``` SEXP data; // my 1D array // I can initialise new 3D vector in the following way: NumericVector vector(Dimension(2, 2, 2); // or the following: NumericVector vector(data.begin(), data.end()); ``` What I didn't figure out is how can I create a NumericVector that would have both my data and the desired dimensions.