On 10 September 2012 at 13:55, Søren Højsgaard wrote:
| Dear list,
|
| I want to do some operations on an array, here exemplified by taking log (the
operations I have in mind are made using RcppArmadillo):
|
| > pp <- array(c(.1, .4, .4, .1), dim=c(2,2),dimnames=list(A=c("a1","a2"),
B=c("b1","b2")))
| > log(pp)
| B
| A b1 b2
| a1 -2.3025851 -0.9162907
| a2 -0.9162907 -2.3025851
|
| It is essential that dim and dimnames attributes are preserved. My take on
this task is:
|
| src <-'
| using namespace arma;
| using namespace Rcpp;
| NumericVector p(pp_);
| // Some computations using RcppArmadillo
| vec pp = as<vec>(pp_);
| vec aa = log(pp);
| // Get the result back
| NumericVector ans(p.length());
| ans = aa;
| // Set attributes
| ans.attr("dim") = p.attr("dim");
| ans.attr("dimnames") = p.attr("dimnames");
| return(wrap(ans));
| '
| > library(inline)
| > loga <- cxxfunction(signature(pp_ = ""), src, plugin = "RcppArmadillo",
verbose=F)
| > loga(pp)
| B
| A b1 b2
| a1 -2.3025851 -0.9162907
| a2 -0.9162907 -2.3025851
|
| This works, but if anyone can spot a more elegant (fewer lines) way of doing
it, I would be happy to know...
All untested and just ideas:
a) Just use Rcpp sugar if all you need is log() etc pp which is present in
sugar; this should preserve attributes
b) First clone the source object to preserve names, dims, ...; then do
transformation and just insert new values
c) If it walks and quacks like a Matrix, ... so use NumericMatrix which does
have a dim attribute
Dirk
|
| Best regards
| Søren
|
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--
Dirk Eddelbuettel | e...@debian.org | http://dirk.eddelbuettel.com
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