Any chance I could ask for an idiots guide for function to.keep(x). I understand how to use it but not what some of the lines are doing. Comments would be extremely helpful. -- View this message in context: http://r.789695.n4.nabble.com/Speeding-up-a-loop-tp4637201p4637316.html Sent from the R help mailing list archive at Nabble.com.