I have created a collection of patches to the R 2.13.0 source that speed up many operations substantially. Some of these are related to the patches I posted in September 2010, though often with additional improvements. Other patches are new. The patches, along with detailed documentation, are available from http://www.cs.utoronto.ca/~radford/R-mods-2.13.0.html For some discussion of these patches and their benefits, see my blog post, at http://radfordneal.wordpress.com/2011/06/09/new-patches-to-speed-up-r-2-13-0 I believe that these improvements to the R implementation should be of substantial benefit to the R community. The R core team is welcome to incorporate them into versions of R that they release in the future. Radford Neal