question on "row.names" attribute of dataframe when called from a compiled package
On Mar 17, 2009, at 16:45 , Whit Armstrong wrote:
Why does the following show a class attribute of "character" when using the interpreter: x <- data.frame(hat=1:10) class(rownames(x)) ## returns [1] "character" but when called from c/cpp, the rownames attribute has no class attribute
Note the difference between class("foo") and attr("foo", "class") -
some classes are implicit.
, and is in fact a vector of INTSXP?
Because the internal representation of automatic row names is c(NA, - dim(d)[1]) where d is the data frame. This is not exposed at the R level, though, since it's an implementation optimization.
.Call("print_class_of_rownames", x, package = "test")
length(x): 10 TYPEOF(x): 13 R_ClassSymbol is null. NULL
is this the intended behaviour?
Yes - it saves a lot of space when using large datasets with automatic names. Cheers, Simon
-Whit
here is my test code:
SEXP print_class_of_rownames(SEXP dataframe_sexp) {
SEXP x = getAttrib(dataframe_sexp,install("row.names"));
cout << "length(x): " << length(x) << endl;
cout << "TYPEOF(x): " << TYPEOF(x) << endl;
if(getAttrib(x, R_ClassSymbol)==R_NilValue) {
cout << "R_ClassSymbol is null." << endl;
} else {
cout << "R_ClassSymbol is a good value." << endl;
}
return R_NilValue;
}
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