Rcpp::DataFrame - find column type

Question

In all Rcpp examples that I could find, one must know the type of DataFrame columns, then you can extract column into vector, e.g.:

// 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"];

In R, one could find column types using sapply() function and class or typeof.

However, I couldn't find the external API in Rcpp responsible for type checking. Is there a way to find column type programmatically?

It seems you need to apply TYPEOF() and R_data_class() over each column; they return a SEXPTYPE and SEXP (STRSXP) respectively. — alexis_laz

Oleg Shirokikh Oleg Shirokikh · Accepted Answer · 2015-11-09T19:42:20

Thanks to Dirk's comment, I found the solution in RcppGallery article:

Dynamic Wrapping and Recursion with Rcpp

TYPEOF and Rf_isFactor should be sufficient to determine the column types of DataFrame. Rinternals.h define the following types, which would be returned by TYPEOF:

#define INTSXP      13    /* integer vectors */
#define REALSXP     14    /* real variables */
#define CPLXSXP     15    /* complex variables */
#define STRSXP      16    /* string vectors */
#define DOTSXP      17    /* dot-dot-dot object */
#define ANYSXP      18    /* make "any" args work. */
#define VECSXP      19    /* generic vectors */
...

Rcpp::DataFrame - find column type

2 Answers