Rcpp：将lfactorial应用于NumericVector

Question

What is the nicest/easiest way to apply the lfactorial function to a NumericVector in Rcpp. In RI would have something like this:

> vec <- c(1,2,3,4)
> lfactorial(vec)
[1] 0.0000000 0.6931472 1.7917595 3.1780538

In Rcpp, suppose I have:

NumericVector vec = NumericVector::create(1,2,3,4);

What is the nicest way to apply Rcpp::internal::lfactorial to each element of vec ?

Thanks for any help.

Answer 1

Rcpp, just like R, is vectorized:

R> cppFunction('NumericVector lfac(NumericVector x) { \
                                        return lfactorial(x); }')
R> lfac(1:4)
[1] 0.000000 0.693147 1.791759 3.178054
R> 

That is one line of code I simply broke for nicer exposition here. Remove the backslash before copying and pasting. You can write it either as a NumericVector or IntegerVector signature.