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#If data (e.g. X) contain missing values (typically, NAs) mean(X) #will return NA mean(X,na.rm=TRUE) #will omit NAs and then do calculation correctly #It is important to remember that if you are developing a function like tapply or lapply that #itself calls functions like mean(), those will also return NAs if you don't make sure that #that tapply/lapply calls the function with na.rm included. #For example, see meanByGroupDS. The line: FUN <- function (x) {UseMethod("mean")} #returns NAs when lapply calls FUN #So you must use: FUN <- function(x) {mean(x,na.rm=TRUE)} |
Paul Burton, 11th June 2015