[Rcpp-devel] trouble creating a dataframe

[Pratibha Rana]

Something seems to go wrong in Vector_create::create__dispatch.

(gdb) p t1
$14 = (const Rcpp::traits::named_object<std::vector<std::basic_string<char,
std::char_traits<char>, std::allocator<char> >,
std::allocator<std::basic_string<char, std::char_traits<char>,
std::allocator<char> > > > > &) @0x7fff5d321780: {name = "datatype", object
= std::vector of length 2, capacity 2 = {"varchar", "varchar"}}

(gdb) p t2
$18 = (const Rcpp::traits::named_object<std::vector<int,
std::allocator<int> > > &) @0x7fff5d321760: {name = "length", object =
std::vector of length 2, capacity 2 = {10, 10}}

(gdb) p t3
$19 = (const Rcpp::traits::named_object<std::vector<int,
std::allocator<int> > > &) @0x7fff5d321740: {name = "scale", object =
std::vector of length 2, capacity 2 = {0, 0}}

(gdb) p res
$17 = {<Rcpp::RObject> = {<No data fields>}, <Rcpp::VectorBase<19, true,
Rcpp::Vector<19> >> = {<Rcpp::traits::expands_to_logical__impl<19>> = {<No
data fields>}, <No data fields>}, <Rcpp::internal::eval_methods<19>> = {<No
data fields>}, cache = {<Rcpp::traits::proxy_cache<19>> = {p = 0x0}, <No
data fields>}}


The value of res was printed at line 159 in Vector__create.h . Using Wrap()
makes it worse. I really need help. I have been trying to do this for 2
days now.


On Mon, Jun 4, 2012 at 4:58 PM, Dirk Eddelbuettel <edd at debian.org> wrote:

>
> Hi Pratibha,
>
> On 4 June 2012 at 16:12, Pratibha Rana wrote:
> | I am at my wits end trying to create  a dataframe from a list of values
> that I
> | have. here's the code
> |
> | try{
> |        int size =  argTypes.getColumnCount();
> |        std::vector<std::string> nameVec(size);
> |        std::vector<int> lenVec(size);
> |        std::vector<int> scaleVec(size);
>
> Good. Three STL vectors which should get autmatic conversion via wrap().
>
> [...]
>
> |        //create the dataframe
> |        Rcpp::List df =
> Rcpp::List::create(Rcpp::Named("datatype",nameVec),
> |                                           Rcpp::Named("length",lenVec),
> |                                           Rcpp::Named("scale",scaleVec));
> |        Rcpp::DataFrame df_final = Rcpp::DataFrame::create(df);
> |        return df_final;
>
> [...]
>
> | The std::vectors are created fine but the list is not created
> | (gdb) p R_PV(df)
> | $3 = 0
> |
> |
> | I have tried a lot of variation like creating the dataframe directly
> without
> | first creating the list. Nothing seems to be working.
>
> It should work. I believe we posted example on the list, blog, possibly in
> RcppExamples, ...
>
>
> In fact, the latter one may be the best key.  Consider this example taken
> straight from the RcppExamples packages (which never became "the"
> collection
> of examples [ contributions welcome ] but has this ...)
>
> RcppExport SEXP RcppDataFrame(SEXP Dsexp) {
>
>    try {                                       // or use BEGIN_RCPP macro
>
>      // construct the data.frame object
>      Rcpp::DataFrame DF = Rcpp::DataFrame(Dsexp);
>
>      // and access each column by name
>      Rcpp::IntegerVector a = DF["a"];
>      Rcpp::CharacterVector b = DF["b"];
>      Rcpp::DateVector c = DF["c"];
>
>      // do something
>      a[2] = 42;
>      b[1] = "foo";
>      c[0] = c[0] + 7;                      // move up a week
>
>      // create a new data frame
>      Rcpp::DataFrame NDF =
>          Rcpp::DataFrame::create(Rcpp::Named("a")=a,
>                                  Rcpp::Named("b")=b,
>                                  Rcpp::Named("c")=c);
>
>      // and return old and new in list
>      return(Rcpp::List::create(Rcpp::Named("origDataFrame")=DF,
>                                Rcpp::Named("newDataFrame")=NDF));
>
>    } catch( std::exception &ex ) {             // or use END_RCPP macro
>        forward_exception_to_r( ex );
>    } catch(...) {
>        ::Rf_error( "c++ exception (unknown reason)" );
>    }
>    return R_NilValue; // -Wall
> }
>
>
> The main difference is that we use Rcpp vectors.  So you could try
>
>  -- wrap() in the create() call
>  -- converting the Rcpp vectors to STL vectors
>  -- debugging why STL vectors don't pass through
>
> Please keep the list posted on your progress.
>
> Dirk
>
> --
> Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com
>
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