[Rcpp-devel] Trailing Index issues, handled as pointer

[John Laing]

Mario,

Your vector matched is 1-indexed, but by passing an element of this vector
(match_id) to rownames[] you're treating it as if it's 0-indexed.

-John





On Mon, Jul 7, 2014 at 10:33 AM, Mario Deng <mariodeng at googlemail.com>
wrote:

> Hello everyone,
>
> I am trying to implement a data structure using Rcpp. But I am already
> struggling with my first method.
> How things (should) work: I want to my function ("createVectorList") a
> data frame or matrix. Each column of the matrix gets sorted. This also
> holds for the rownames - storing the sorted rownames for each sort column
> gives me big memory footprint, but log(n) access while reading later.
> Basically everything is fine, but when accessing some data through a for
> loop I get "address 0x0, cause 'memory not mapped'".
>
> Here is my Code:
>
> #include <Rcpp.h>
> using namespace Rcpp;
>
> // [[Rcpp::export]]
> List createVectorList(NumericMatrix df, CharacterVector rownames) {
>   List sorted_rownames(df.ncol());
>   for(int i = 0; i < df.ncol(); i++){
>     NumericVector sorted_vec = df(_,i);
>     std::sort(sorted_vec.begin(), sorted_vec.end());
>     NumericVector one_col = df(_,i);
>     df(_,i)=sorted_vec;
>     IntegerVector matched = match( sorted_vec, one_col);
>     CharacterVector one_sorted_row(df.nrow());
>     for(int j = 0; j < one_sorted_row.length(); j++){
>       int match_id=matched[j];
>       String r_name=rownames[match_id];
>       one_sorted_row[j]=r_name;
>     }
>     sorted_rownames[i]=one_sorted_row;
>   }
>   return Rcpp::List::create(Rcpp::Named("Matrix") = df,
> Rcpp::Named("rowIDX")=sorted_rownames);
> }
>
> There trouble is within these lines:
>
>     for(int j = 0; j < one_sorted_row.length(); j++){
>       int match_id=matched[j];
>       String r_name=rownames[match_id];
>       one_sorted_row[j]=r_name;
>     }
>
> When executing this, I get the error named above.
> What I thought about: rownames should be of the type "Proxy" or so, maybe
> thats the point?
>
> Maybe one of you has a hint.
>
> With beste regards,
>
> Mario
> __
> MD
> mariodeng at googlemail.com
>
>
>
>
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