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

[Romain Francois]

Should work as expected with the next version of Rcpp (svn version >= 
3000).

require( Rcpp )
require( inline )
df <- data.frame(
     V1 = c("c3", "c1", "c2" ),
     V2 = c("3a", "1b", "2c" )
     )
fx <- cxxfunction( signature( x = "data.frame" ), '
     DataFrame DF(x);
     StringVector v1 = DF["V1"];
     StringVector v2 = DF["V2"] ;
     return List::create( v1, v2) ;
' , plugin = "Rcpp" )


 > fx( df )
[[1]]
[1] "c3" "c1" "c2"

[[2]]
[1] "3a" "1b" "2c"

Romain


Le 12/04/11 12:38, deqiang sun a écrit :
> 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?
>
> 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
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>>
>>
>
>


-- 
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