[Rcpp-devel] data.frame from R to C++?

[deqiang sun]

Thanks, the stringsAsFactors=FALSE option works.

Dsun
On Apr 12, 2011, at 6:36 AM, Dirk Eddelbuettel wrote:

> 
> On 12 April 2011 at 05:38, deqiang sun wrote:
> | How should I read the txt in the following context?
> | c3	3a
> | c1	1b
> | c2	2c
> | 
> | The code I have is 
> | 		RInside R(argc, argv);
> | 		SEXP ans;
> | 
> | 		std::string txt = "a=read.csv('xxx.xls',sep='\t',head=F)";
> | 		ans = R.parseEval(txt);
> | 		Rcpp::DataFrame DF(ans);
> | 
> | 		Rcpp::StringVector x1 = DF["V1"];
> | 		Rcpp::StringVector x2 = DF["V2"];
> | 
> | But the print of x1 and x2 is 
> | 3	3	
> | 1	1	
> | 2	2	
> | 
> | What's wrong with my code?
> 
> The read.csv() function and its cousins default to stringsAsFactors=TRUE. 
> 
> So the '3 1 2' are the factor levels. You want either 
> 
>    std::string txt = "a=read.csv('xxx.xls',sep='\t',"
>                      "head=FALSE,stringsAsFactors=FALSE)";
> 
> or set it as a global option.  Google for stringsAsFactors, this is
> documented and are ways around it.  
> 
> Dirk
> 
> PS  I personally would also set column names in the data file or R code.
> 
> 
> | Thanks,
> | 
> | Dsun
> | On Apr 12, 2011, at 4:14 AM, Romain Francois wrote:
> | 
> | > Le 12/04/11 10:57, deqiang sun a écrit :
> | >> Hi Dirk,
> | >> 
> | >> Thanks very much for your example. From this example I learned how to passing data back and forth between R and C++.
> | >> The example is R code and uses piece of C++ code in side R program.
> | >> Well, it's better if you put this example(by only making slight changes to make R embeded in C++) inside package RInside.
> | >> 
> | >> Accessing data by column name is the feature I ( and other people) usually want.
> | >> However, is there a way to access the data Frame by row number?
> | > 
> | > No. You access the column, and then do whatever with each element, as in 
> | > Dirk's example.
> | > 
> | >> Regards.
> | >> 
> | >> Dsun
> | >> On Apr 8, 2011, at 9:56 AM, Dirk Eddelbuettel wrote:
> | >> 
> | >>> 
> | >>> Ok, I now committed a slightly nice example to RcppExamples, a package I
> | >>> should revamp to contain more examples.  In there, we now receive a
> | >>> data.frame, operate on each column, create a new data and return old and new.
> | >>> 
> | >>> The core of the code (inside the try/catch protection) is
> | >>> 
> | >>>      // 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));
> | >>> 
> | >>> 
> | >>> Dirk
> | >>> --
> | >>> Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com
> | > 
> | > -- 
> | > Romain Francois
> | > Professional R Enthusiast
> | > +33(0) 6 28 91 30 30
> | > http://romainfrancois.blog.free.fr
> | > http://romain-francois.com
> | > |- http://bit.ly/fhqbRC : Rcpp workshop in Chicago on April 28th
> | > |- http://bit.ly/dFyZGB : Hydraulique au Montpellier Comedie Club
> | > `- http://bit.ly/eVXit9 : Eponyme : 40 minutes stand up
> | > 
> | > 
> | 
> 
> -- 
> Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com