In preparing for my upcoming Rcpp talk at the Oslo useR! Group, I started wondering how much of R is actually written in C or Fortran. I have of course been trained to think that vectorization is great, because then you let C or Fortran do the job, but how much of R is actually written in these languages? Some searching led me to this blog, which analyzes R-2.13.1. However, that post is from 2011, and at the time of writing R has reached version 3-5.