Oops, tiny mistake. Try lapply(X = b, FUN = function(x) { swn <- seq(from = 0, to = (0 + 0.01*length(x))-0.01, by = 0.01) out <- x + swn return(out) }) -- View this message in context: http://r.789695.n4.nabble.com/help-program-efficiency-tp3059079p3060806.html Sent from the R help mailing list archive at Nabble.com.