# [Rcpp-devel] Three-dimensional vectors example

Dirk Eddelbuettel edd at debian.org
Mon Sep 24 20:50:10 CEST 2012

```Someone just asked on StackOverflow about creating 3d arrays:
http://stackoverflow.com/questions/12569992/constructing-3d-array-in-rcpp

The best I could come up with is below. Did I miss something better?

Full disclosure: The last I needed this, I also needed ops on it, and used

Dirk

File:

library(inline)

fx <- cxxfunction(signature(vs="numeric", ds="integer"), plugin="Rcpp", body='
Rcpp::NumericVector v(vs);           	// get the data
Rcpp::Dimension d(ds);               	// get the dimension object
Rcpp::NumericVector r(d);            	// create (empty) vector with correct dims
std::copy(v.begin(), v.end(), r.begin()); 	// and copy
return Rcpp::List::create(v, d, r);
')

Output:

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 dimension object
+    Rcpp::NumericVector r(d);             // create (empty) vector 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>

--
Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com
```