Some rules of thumb for new R users (According to myself): If you are working with data.frame s, forget there is a function called apply - whatever you do - don`t use it. Especially with a margin of 1 (the only good usecase for this function is to operate over matrix columns- margin of 2). Some good alternatives: ?do.call , ?pmax/pmin , ?max.col , ?rowSums/rowMeans/etc , the awesome matrixStats packages (for matrices), ?rowsum and many more For loops are not bad- don`t listen to anyone who says otherwise. They are bad only in certain cases: If you use them to iterate over rows. If you are performing unvectorized/inefficient operation within each iteration If you are writing a loop for something that is already vectorized R is a vectorized language- meaning many operation were already written in C loops- so don`t reinvent the wheel and write stuff in R loops if it was already written. With one exception- many of these functions work only with matrices. Hence, if you have a data.frame you should think twice if you want it to be converted to a matrix (you may experience some unexpected consequences as a result), or can you avoid it. Learn base R before you learn any fancy packages such as dplyr . It is a nice package and all, but it was designed for very specific things. Many many operations could be done much more efficiently using base R. Get familiar with R classes. Learn what is factor and how to use it. Know the difference between a matrix (a vector with a dim attribute) and a data.frame (a list of vectors). Learn how and when to work with list s or array s. Know the difference between numeric and integer . Read about floating points. Learn how and when yo use lapply/sapply/vapply - these could come useful many times You must learn some ?regex . Must. Read ?S4groupGeneric in order to discover which functions have data.frame methods (a very useful to know). Learn about ?methods Read ?strptime very carefully (note the Sys.setlocale("LC_TIME", "C") part - could be a life saver). Read the damn docs. R has awesome documentation- please use it. You won`t find anything even nearly as good in any other language (I know of). Like Barry Rowlingson once said: "This is all documented in TFM. Those who WTFM don`t want to have to WTFM again on the mailing list. RTFM." Profile ©