A Need for Speed R often receives (unfair) criticism of being slow. In some cases this is true but often this is simply due to how the code is written and which packages are being leveraged. The R language is fast when vectorized functions are used (e.g. mean()), which avoids coding for loops in R. However, sometimes a problem is simply easier to code and understand when written as a loop; this is especially the case when the loops are nested.