Error: Unable to convert using R function: as.data.frame
I am trying to read a text file in C ++ and return it as a DataFrame. I created a skeleton method to read a file and return it:
// [[Rcpp::export]]
DataFrame rcpp_hello_world(String fileName) {
int vsize = get_number_records(fileName);
CharacterVector field1 = CharacterVector(vsize+1);
std::ifstream in(fileName);
int i = 0;
string tmp;
while (!in.eof()) {
getline(in, tmp, '\n');
field1[i] = tmp;
tmp.clear( );
i++;
}
DataFrame df(field1);
return df;
}
I am running in R using:
> df <- rcpp_hello_world( "my_haproxy_logfile" )
However, R returns the following error:
Error: could not convert using R function : as.data.frame
What am I doing wrong?
Many thanks.
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1 answer
DataFrame objects are "special". Our preferred use is through return Rcpp::DateFrame::create ...
, which you'll see in many examples posted, including numerous answers here.
Here is one from the Rcpp gallery post :
#include <Rcpp.h>
using namespace Rcpp;
// [[Rcpp::export]]
DataFrame modifyDataFrame(DataFrame df) {
// access the columns
Rcpp::IntegerVector a = df["a"];
Rcpp::CharacterVector b = df["b"];
// make some changes
a[2] = 42;
b[1] = "foo";
// return a new data frame
return DataFrame::create(_["a"]= a, _["b"]= b);
}
Focused on modifying the DataFrame, it shows you how to create it. The label _["a"]
can also be written as Named("a")
which I prefer.
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