[Rcpp-devel] trouble creating a dataframe

[Dirk Eddelbuettel]

On 4 June 2012 at 17:28, Pratibha Rana wrote:
| 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.

What about the working example I just to the list?

What about the following adapted from the unit test file for dataframes:


R> library(inline)
R> 
R> fx <- cxxfunction(signature(), plugin="Rcpp", body='
+     IntegerVector v = IntegerVector::create(1,2,3);
+     std::vector<std::string> s(3);
+     s[0] = "a";
+     s[1] = "b";
+     s[2] = "c";
+     return DataFrame::create(Named("a")=v, Named("b")=s);
+ ')
R> 
R> fx()
  a b
1 1 a
2 2 b
3 3 c
R> 


I usually start from self-contained working examples and then try to
generalise to the specific issue at hand.

Hope this helps,  Dirk
 
 
| 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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-- 
Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com