Efficient alternatives to merge for larger data.frames R

Question

I am looking for an efficient (both computer resource wise and learning/implementation wise) method to merge two larger (size>1 million / 300 KB RData file) data frames.

Answer 1

Do you have to do the merge in R? If not, merge the underlying data files using a simple file concatenation and then load them into R. (I realize this may not apply to your situation -- but if it does, it could save you a lot of headache.)