[Rcpp-devel] Bug or intended behaviour?

[Søren Højsgaard]

Ooooops; just realised that I did not allocate memory inside the loop; now it works:

// [[Rcpp::export]]
List do_colmat2list_str(SEXP XX_)
{
  CharacterMatrix X(XX_);
  int nc=X.ncol(), nr=X.nrow(), k;
  List out(nc);
  for (int j=0; j<nc; j++){
    CharacterVector v(nr);
    for (k=0; k<nr; ++k){
      v[ k ] = X( k, j);
    }
    out(j) =  v ; 
  }
  return out;
}

Sorry for the trouble...
Søren



-----Original Message-----
From: rcpp-devel-bounces at lists.r-forge.r-project.org [mailto:rcpp-devel-bounces at lists.r-forge.r-project.org] On Behalf Of Søren Højsgaard
Sent: 18. marts 2014 07:59
To: rcpp-devel at lists.r-forge.r-project.org (rcpp-devel at r-forge.wu-wien.ac.at)
Subject: [Rcpp-devel] Bug or intended behaviour?

Dear all

I want to split a matrix with characters into a list "by columns", for example:

m2 <- matrix(letters[1:16], 4); m2
     [,1] [,2] [,3] [,4]
[1,] "a"  "e"  "i"  "m" 
[2,] "b"  "f"  "j"  "n" 
[3,] "c"  "g"  "k"  "o" 
[4,] "d"  "h"  "l"  "p"

I do:

// [[Rcpp::export]]
List do_colmat2list_str(SEXP XX_)
{
  CharacterMatrix X(XX_);
  int nc=X.ncol(), nr=X.nrow(), k;
  CharacterVector v(nr);
  List out(nc);
  for (int j=0; j<nc; j++){
    for (k=0; k<nr; ++k){
      v[ k ] = X( k, j);
    }
    Rprintf("current v:"); Rf_PrintValue( v );
    out(j) = v;
  }
  return out;
}

And I get the following result (which surprises me):

do_colmat2list_str(m2)
current v:[1] "a" "b" "c" "d"
current v:[1] "e" "f" "g" "h"
current v:[1] "i" "j" "k" "l"
current v:[1] "m" "n" "o" "p"
[[1]]
[1] "m" "n" "o" "p"
[[2]]
[1] "m" "n" "o" "p"
[[3]]
[1] "m" "n" "o" "p"
[[4]]
[1] "m" "n" "o" "p"

If I clone v before "sticking it into" out I get the result I expect:

// [[Rcpp::export]]
List do_colmat2list_str(SEXP XX_)
{
  CharacterMatrix X(XX_);
  int nc=X.ncol(), nr=X.nrow(), k;
  CharacterVector v(nr);
  List out(nc);
  for (int j=0; j<nc; j++){
    for (k=0; k<nr; ++k){
      v[ k ] = X( k, j);
    }
    Rprintf("current v:"); Rf_PrintValue( v );
    out(j) = clone( v );  // here we clone...........
  }
  return out;
}

do_colmat2list_str(m2)
current v:[1] "a" "b" "c" "d"
current v:[1] "e" "f" "g" "h"
current v:[1] "i" "j" "k" "l"
current v:[1] "m" "n" "o" "p"
[[1]]
[1] "a" "b" "c" "d"
[[2]]
[1] "e" "f" "g" "h"
[[3]]
[1] "i" "j" "k" "l"
[[4]]
[1] "m" "n" "o" "p"


Is this how things are supposed to work, or is there a memory issue somewhere??

Cheers
Søren

sessionInfo()
R version 3.0.3 Patched (2014-03-06 r65198)
Platform: x86_64-w64-mingw32/x64 (64-bit)

locale:
[1] LC_COLLATE=Danish_Denmark.1252  LC_CTYPE=Danish_Denmark.1252    LC_MONETARY=Danish_Denmark.1252
[4] LC_NUMERIC=C                    LC_TIME=Danish_Denmark.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] Rcpp_0.11.1    devtools_1.4.1 shTools_1.0    markdown_0.6.4 knitr_1.5     

loaded via a namespace (and not attached):
 [1] compiler_3.0.3 digest_0.6.4   evaluate_0.5.1 formatR_0.10   httr_0.2       memoise_0.1    parallel_3.0.3
 [8] RCurl_1.95-4.1 stringr_0.6.2  tools_3.0.3    whisker_0.3-2






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