I noticed a difference in how as.POSIXct handled the 'format' argument when 'x' is character versus when 'x' is a factor. For example: myFormat <- "%d-%m-%Y" myDateStr <- format(Sys.Date()+1:5,myFormat) as.POSIXct(myDateStr, format=myFormat) as.POSIXct(factor(myDateStr), format=myFormat) It seems to be caused by '...' not being passed in as.POSIXlt.factor. Would it make sense to change the function to pass '...'? I.e. from: as.POSIXlt.factor <- function(x, ...) as.POSIXlt(as.character(x)) to: as.POSIXlt.factor <- function(x, ...) as.POSIXlt(as.character(x), ...) Regards, -- Joshua Ulrich ?| ?FOSS Trading: www.fosstrading.com