reshape2 1.4 is now available on CRAN. This version adds a number of useful arguments and messages, but mostly importantly it gains a C++ implementation of melt.data.frame(). This new method should be much much faster (>10x) and does a better job of preserving existing attributes. For full details, see the release notes on github.

The C++ implementation of melt was contributed by Kevin Ushey , who we’re very pleased to announce has joined RStudio. You may be familiar with Kevin from his contributions to Rcpp, or his CRAN packages Kmisc and timeit.