On 31 July 2018 at 13:55, Barth Riley wrote:
| Dear list
|
| I am trying to create a simple Rcpp function that creates a three-dimensional
array based on the values of a four-dimensional array. The arrays are declared
as NumericVectors with a dim attribute represent the number of levels of each
dimension. Here is a sample of the code:
|
| NumericVector sumby4(NumericVector X) {
| Dimension dim = X.attr("dim");
| if(dim.size() != 4) return NULL;
|
| NumericVector ret = NumericVector::create(dim[0],dim[1],dim[2]);
|
| for(int i = 0; i < dim[0]; i++) {
| for(int j = 0; j < dim[1]; j++) {
| for(int k = 0; k < dim[2]; k++) {
| ret(i,j,k) = NA_REAL;
| …
|
| When I attempt to compile the package in which this function resides, I get
the error message associated with the “ret(I,j,k) = NA_REAL” line:
|
| No match for call to Rcpp::NumericVector Rcpp::Vector<14
Rcpp::PreserveStorage>})(int&, int&, int&)
|
| I take from this message that the NumericVector ret cannot be indexed by
three values, even though it has been dimensioned as a 3D array. What am I
doing wrong here?
Yes, the compiler barks because it sees no matching method.
Now, we _have_ examples for this somewhere I think. One thing that came up in a
quick search is
http://gallery.rcpp.org/articles/simple-array-class/
and you can see there that i) yes a multi-dim is used but ii) indexing games
need to be played. Maybe that helps.
Else arma::cube is a real 3d data I have used happily in the past. And these
days CRAN has xtensor (if you can do C++14).
Dirk
--
http://dirk.eddelbuettel.com | @eddelbuettel | e...@debian.org
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