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 | e...@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 | e...@debian.org | http://dirk.eddelbuettel.com
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