we always feel difficulty in dealing with some R codes,now share some very useful methods to improve it from Noam Ross:

• Get a bigger computer (for example, renting an instance on the Amazon cloud for a few cents an hour)
• Use parallel programming techniques
• Using the R byte-compiler
• Profiling and benchmarking your code
• Using high-performance packages (like xts, for time series)
• And lastly, rewriting your code to use more efficient constructs.
• detail information,you can read FasteR! HigheR! StrongeR! - A Guide to Speeding Up R Code for Busy People